diff --git a/tests/PhpSpreadsheetTests/Calculation/DateTimeTest.php b/tests/PhpSpreadsheetTests/Calculation/DateTimeTest.php
index 6b05d454..8959cb00 100644
--- a/tests/PhpSpreadsheetTests/Calculation/DateTimeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/DateTimeTest.php
@@ -25,7 +25,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testDATE($expectedResult, ...$args)
     {
         $result = DateTime::DATE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDATE()
@@ -38,7 +38,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::DATE(2012, 1, 31);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(1327968000, $result, null, 1E-8);
+        self::assertEquals(1327968000, $result, null, 1E-8);
     }
 
     public function testDATEtoPHPObject()
@@ -47,11 +47,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::DATE(2012, 1, 31);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('d-M-Y'), '31-Jan-2012');
+        self::assertEquals($result->format('d-M-Y'), '31-Jan-2012');
     }
 
     public function testDATEwith1904Calendar()
@@ -59,7 +59,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
         $result = DateTime::DATE(1918, 11, 11);
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
-        $this->assertEquals($result, 5428);
+        self::assertEquals($result, 5428);
     }
 
     public function testDATEwith1904CalendarError()
@@ -67,7 +67,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
         $result = DateTime::DATE(1901, 1, 31);
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
-        $this->assertEquals($result, '#NUM!');
+        self::assertEquals($result, '#NUM!');
     }
 
     /**
@@ -78,7 +78,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testDATEVALUE($expectedResult, ...$args)
     {
         $result = DateTime::DATEVALUE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDATEVALUE()
@@ -91,7 +91,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::DATEVALUE('2012-1-31');
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(1327968000, $result, null, 1E-8);
+        self::assertEquals(1327968000, $result, null, 1E-8);
     }
 
     public function testDATEVALUEtoPHPObject()
@@ -100,11 +100,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::DATEVALUE('2012-1-31');
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('d-M-Y'), '31-Jan-2012');
+        self::assertEquals($result->format('d-M-Y'), '31-Jan-2012');
     }
 
     /**
@@ -115,7 +115,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testYEAR($expectedResult, ...$args)
     {
         $result = DateTime::YEAR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerYEAR()
@@ -131,7 +131,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testMONTH($expectedResult, ...$args)
     {
         $result = DateTime::MONTHOFYEAR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerMONTH()
@@ -147,7 +147,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testWEEKNUM($expectedResult, ...$args)
     {
         $result = DateTime::WEEKNUM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerWEEKNUM()
@@ -163,7 +163,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testWEEKDAY($expectedResult, ...$args)
     {
         $result = DateTime::WEEKDAY(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerWEEKDAY()
@@ -179,7 +179,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testDAY($expectedResult, ...$args)
     {
         $result = DateTime::DAYOFMONTH(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDAY()
@@ -195,7 +195,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testTIME($expectedResult, ...$args)
     {
         $result = DateTime::TIME(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerTIME()
@@ -208,7 +208,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::TIME(7, 30, 20);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(27020, $result, null, 1E-8);
+        self::assertEquals(27020, $result, null, 1E-8);
     }
 
     public function testTIMEtoPHPObject()
@@ -217,11 +217,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::TIME(7, 30, 20);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('H:i:s'), '07:30:20');
+        self::assertEquals($result->format('H:i:s'), '07:30:20');
     }
 
     /**
@@ -232,7 +232,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testTIMEVALUE($expectedResult, ...$args)
     {
         $result = DateTime::TIMEVALUE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerTIMEVALUE()
@@ -245,7 +245,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::TIMEVALUE('7:30:20');
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(23420, $result, null, 1E-8);
+        self::assertEquals(23420, $result, null, 1E-8);
     }
 
     public function testTIMEVALUEtoPHPObject()
@@ -254,11 +254,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::TIMEVALUE('7:30:20');
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('H:i:s'), '07:30:20');
+        self::assertEquals($result->format('H:i:s'), '07:30:20');
     }
 
     /**
@@ -269,7 +269,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testHOUR($expectedResult, ...$args)
     {
         $result = DateTime::HOUROFDAY(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerHOUR()
@@ -285,7 +285,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testMINUTE($expectedResult, ...$args)
     {
         $result = DateTime::MINUTE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerMINUTE()
@@ -301,7 +301,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testSECOND($expectedResult, ...$args)
     {
         $result = DateTime::SECOND(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerSECOND()
@@ -317,7 +317,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testNETWORKDAYS($expectedResult, ...$args)
     {
         $result = DateTime::NETWORKDAYS(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerNETWORKDAYS()
@@ -333,7 +333,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testWORKDAY($expectedResult, ...$args)
     {
         $result = DateTime::WORKDAY(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerWORKDAY()
@@ -349,7 +349,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testEDATE($expectedResult, ...$args)
     {
         $result = DateTime::EDATE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerEDATE()
@@ -362,7 +362,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::EDATE('2012-1-26', -1);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(1324857600, $result, null, 1E-8);
+        self::assertEquals(1324857600, $result, null, 1E-8);
     }
 
     public function testEDATEtoPHPObject()
@@ -371,11 +371,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::EDATE('2012-1-26', -1);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('d-M-Y'), '26-Dec-2011');
+        self::assertEquals($result->format('d-M-Y'), '26-Dec-2011');
     }
 
     /**
@@ -386,7 +386,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testEOMONTH($expectedResult, ...$args)
     {
         $result = DateTime::EOMONTH(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerEOMONTH()
@@ -399,7 +399,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         Functions::setReturnDateType(Functions::RETURNDATE_PHP_NUMERIC);
         $result = DateTime::EOMONTH('2012-1-26', -1);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        $this->assertEquals(1325289600, $result, null, 1E-8);
+        self::assertEquals(1325289600, $result, null, 1E-8);
     }
 
     public function testEOMONTHtoPHPObject()
@@ -408,11 +408,11 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
         $result = DateTime::EOMONTH('2012-1-26', -1);
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         //    Must return an object...
-        $this->assertInternalType('object', $result);
+        self::assertInternalType('object', $result);
         //    ... of the correct type
-        $this->assertTrue(is_a($result, 'DateTime'));
+        self::assertTrue(is_a($result, 'DateTime'));
         //    ... with the correct value
-        $this->assertEquals($result->format('d-M-Y'), '31-Dec-2011');
+        self::assertEquals($result->format('d-M-Y'), '31-Dec-2011');
     }
 
     /**
@@ -423,7 +423,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testDATEDIF($expectedResult, ...$args)
     {
         $result = DateTime::DATEDIF(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDATEDIF()
@@ -439,7 +439,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testDAYS360($expectedResult, ...$args)
     {
         $result = DateTime::DAYS360(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDAYS360()
@@ -455,7 +455,7 @@ class DateTimeTest extends PHPUnit_Framework_TestCase
     public function testYEARFRAC($expectedResult, ...$args)
     {
         $result = DateTime::YEARFRAC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerYEARFRAC()
diff --git a/tests/PhpSpreadsheetTests/Calculation/EngineeringTest.php b/tests/PhpSpreadsheetTests/Calculation/EngineeringTest.php
index 2e19eff7..eab13cd6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/EngineeringTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/EngineeringTest.php
@@ -33,7 +33,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBESSELI($expectedResult, ...$args)
     {
         $result = Engineering::BESSELI(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerBESSELI()
@@ -49,7 +49,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBESSELJ($expectedResult, ...$args)
     {
         $result = Engineering::BESSELJ(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerBESSELJ()
@@ -65,7 +65,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBESSELK($expectedResult, ...$args)
     {
         $result = Engineering::BESSELK(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerBESSELK()
@@ -81,7 +81,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBESSELY($expectedResult, ...$args)
     {
         $result = Engineering::BESSELY(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerBESSELY()
@@ -97,7 +97,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testCOMPLEX($expectedResult, ...$args)
     {
         $result = Engineering::COMPLEX(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCOMPLEX()
@@ -113,7 +113,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMAGINARY($expectedResult, ...$args)
     {
         $result = Engineering::IMAGINARY(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIMAGINARY()
@@ -129,7 +129,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMREAL($expectedResult, ...$args)
     {
         $result = Engineering::IMREAL(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIMREAL()
@@ -145,7 +145,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMABS($expectedResult, ...$args)
     {
         $result = Engineering::IMABS(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIMABS()
@@ -162,7 +162,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMARGUMENT($expectedResult, ...$args)
     {
         $result = Engineering::IMARGUMENT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIMARGUMENT()
@@ -178,7 +178,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMCONJUGATE($expectedResult, ...$args)
     {
         $result = Engineering::IMCONJUGATE(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMCONJUGATE()
@@ -194,7 +194,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMCOS($expectedResult, ...$args)
     {
         $result = Engineering::IMCOS(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMCOS()
@@ -213,7 +213,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Engineering::IMDIV(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMDIV()
@@ -229,7 +229,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMEXP($expectedResult, ...$args)
     {
         $result = Engineering::IMEXP(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMEXP()
@@ -245,7 +245,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMLN($expectedResult, ...$args)
     {
         $result = Engineering::IMLN(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMLN()
@@ -261,7 +261,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMLOG2($expectedResult, ...$args)
     {
         $result = Engineering::IMLOG2(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMLOG2()
@@ -277,7 +277,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMLOG10($expectedResult, ...$args)
     {
         $result = Engineering::IMLOG10(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMLOG10()
@@ -296,7 +296,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Engineering::IMPOWER(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMPOWER()
@@ -312,7 +312,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMPRODUCT($expectedResult, ...$args)
     {
         $result = Engineering::IMPRODUCT(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMPRODUCT()
@@ -328,7 +328,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMSIN($expectedResult, ...$args)
     {
         $result = Engineering::IMSIN(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMSIN()
@@ -344,7 +344,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMSQRT($expectedResult, ...$args)
     {
         $result = Engineering::IMSQRT(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMSQRT()
@@ -363,7 +363,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Engineering::IMSUB(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMSUB()
@@ -380,7 +380,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testIMSUM($expectedResult, ...$args)
     {
         $result = Engineering::IMSUM(...$args);
-        $this->assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
+        self::assertTrue($this->complexAssert->assertComplexEquals($expectedResult, $result, 1E-8), $this->complexAssert->getErrorMessage());
     }
 
     public function providerIMSUM()
@@ -396,7 +396,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testERF($expectedResult, ...$args)
     {
         $result = Engineering::ERF(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerERF()
@@ -412,7 +412,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testERFC($expectedResult, ...$args)
     {
         $result = Engineering::ERFC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerERFC()
@@ -428,7 +428,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBIN2DEC($expectedResult, ...$args)
     {
         $result = Engineering::BINTODEC(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerBIN2DEC()
@@ -444,7 +444,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBIN2HEX($expectedResult, ...$args)
     {
         $result = Engineering::BINTOHEX(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerBIN2HEX()
@@ -460,7 +460,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testBIN2OCT($expectedResult, ...$args)
     {
         $result = Engineering::BINTOOCT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerBIN2OCT()
@@ -476,7 +476,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testDEC2BIN($expectedResult, ...$args)
     {
         $result = Engineering::DECTOBIN(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerDEC2BIN()
@@ -492,7 +492,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testDEC2HEX($expectedResult, ...$args)
     {
         $result = Engineering::DECTOHEX(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerDEC2HEX()
@@ -508,7 +508,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testDEC2OCT($expectedResult, ...$args)
     {
         $result = Engineering::DECTOOCT(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerDEC2OCT()
@@ -524,7 +524,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testHEX2BIN($expectedResult, ...$args)
     {
         $result = Engineering::HEXTOBIN(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerHEX2BIN()
@@ -540,7 +540,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testHEX2DEC($expectedResult, ...$args)
     {
         $result = Engineering::HEXTODEC(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerHEX2DEC()
@@ -556,7 +556,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testHEX2OCT($expectedResult, ...$args)
     {
         $result = Engineering::HEXTOOCT(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerHEX2OCT()
@@ -572,7 +572,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testOCT2BIN($expectedResult, ...$args)
     {
         $result = Engineering::OCTTOBIN(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerOCT2BIN()
@@ -588,7 +588,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testOCT2DEC($expectedResult, ...$args)
     {
         $result = Engineering::OCTTODEC(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerOCT2DEC()
@@ -604,7 +604,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testOCT2HEX($expectedResult, ...$args)
     {
         $result = Engineering::OCTTOHEX(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerOCT2HEX()
@@ -620,7 +620,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testDELTA($expectedResult, ...$args)
     {
         $result = Engineering::DELTA(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerDELTA()
@@ -636,7 +636,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testGESTEP($expectedResult, ...$args)
     {
         $result = Engineering::GESTEP(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerGESTEP()
@@ -647,25 +647,25 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testGetConversionGroups()
     {
         $result = Engineering::getConversionGroups();
-        $this->assertInternalType('array', $result);
+        self::assertInternalType('array', $result);
     }
 
     public function testGetConversionGroupUnits()
     {
         $result = Engineering::getConversionGroupUnits();
-        $this->assertInternalType('array', $result);
+        self::assertInternalType('array', $result);
     }
 
     public function testGetConversionGroupUnitDetails()
     {
         $result = Engineering::getConversionGroupUnitDetails();
-        $this->assertInternalType('array', $result);
+        self::assertInternalType('array', $result);
     }
 
     public function testGetConversionMultipliers()
     {
         $result = Engineering::getConversionMultipliers();
-        $this->assertInternalType('array', $result);
+        self::assertInternalType('array', $result);
     }
 
     /**
@@ -676,7 +676,7 @@ class EngineeringTest extends PHPUnit_Framework_TestCase
     public function testCONVERTUOM($expectedResult, ...$args)
     {
         $result = Engineering::CONVERTUOM(...$args);
-        $this->assertEquals($expectedResult, $result, null);
+        self::assertEquals($expectedResult, $result, null);
     }
 
     public function providerCONVERTUOM()
diff --git a/tests/PhpSpreadsheetTests/Calculation/FinancialTest.php b/tests/PhpSpreadsheetTests/Calculation/FinancialTest.php
index 04f6b4e8..d780e014 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FinancialTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FinancialTest.php
@@ -22,7 +22,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testACCRINT($expectedResult, ...$args)
     {
         $result = Financial::ACCRINT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerACCRINT()
@@ -38,7 +38,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testACCRINTM($expectedResult, ...$args)
     {
         $result = Financial::ACCRINTM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerACCRINTM()
@@ -54,7 +54,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testAMORDEGRC($expectedResult, ...$args)
     {
         $result = Financial::AMORDEGRC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerAMORDEGRC()
@@ -70,7 +70,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testAMORLINC($expectedResult, ...$args)
     {
         $result = Financial::AMORLINC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerAMORLINC()
@@ -86,7 +86,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPDAYBS($expectedResult, ...$args)
     {
         $result = Financial::COUPDAYBS(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPDAYBS()
@@ -102,7 +102,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPDAYS($expectedResult, ...$args)
     {
         $result = Financial::COUPDAYS(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPDAYS()
@@ -118,7 +118,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPDAYSNC($expectedResult, ...$args)
     {
         $result = Financial::COUPDAYSNC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPDAYSNC()
@@ -134,7 +134,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPNCD($expectedResult, ...$args)
     {
         $result = Financial::COUPNCD(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPNCD()
@@ -150,7 +150,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPNUM($expectedResult, ...$args)
     {
         $result = Financial::COUPNUM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPNUM()
@@ -166,7 +166,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCOUPPCD($expectedResult, ...$args)
     {
         $result = Financial::COUPPCD(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCOUPPCD()
@@ -182,7 +182,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCUMIPMT($expectedResult, ...$args)
     {
         $result = Financial::CUMIPMT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCUMIPMT()
@@ -198,7 +198,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testCUMPRINC($expectedResult, ...$args)
     {
         $result = Financial::CUMPRINC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerCUMPRINC()
@@ -214,7 +214,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testDB($expectedResult, ...$args)
     {
         $result = Financial::DB(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDB()
@@ -230,7 +230,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testDDB($expectedResult, ...$args)
     {
         $result = Financial::DDB(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDDB()
@@ -246,7 +246,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testDISC($expectedResult, ...$args)
     {
         $result = Financial::DISC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDISC()
@@ -262,7 +262,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testDOLLARDE($expectedResult, ...$args)
     {
         $result = Financial::DOLLARDE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDOLLARDE()
@@ -278,7 +278,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testDOLLARFR($expectedResult, ...$args)
     {
         $result = Financial::DOLLARFR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerDOLLARFR()
@@ -294,7 +294,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testEFFECT($expectedResult, ...$args)
     {
         $result = Financial::EFFECT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerEFFECT()
@@ -310,7 +310,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testFV($expectedResult, ...$args)
     {
         $result = Financial::FV(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerFV()
@@ -326,7 +326,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testFVSCHEDULE($expectedResult, ...$args)
     {
         $result = Financial::FVSCHEDULE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerFVSCHEDULE()
@@ -342,7 +342,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testINTRATE($expectedResult, ...$args)
     {
         $result = Financial::INTRATE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerINTRATE()
@@ -358,7 +358,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testIPMT($expectedResult, ...$args)
     {
         $result = Financial::IPMT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIPMT()
@@ -374,7 +374,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testIRR($expectedResult, ...$args)
     {
         $result = Financial::IRR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIRR()
@@ -390,7 +390,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testISPMT($expectedResult, ...$args)
     {
         $result = Financial::ISPMT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerISPMT()
@@ -406,7 +406,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testMIRR($expectedResult, ...$args)
     {
         $result = Financial::MIRR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerMIRR()
@@ -422,7 +422,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testNOMINAL($expectedResult, ...$args)
     {
         $result = Financial::NOMINAL(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerNOMINAL()
@@ -438,7 +438,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testNPER($expectedResult, ...$args)
     {
         $result = Financial::NPER(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerNPER()
@@ -454,7 +454,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
     public function testNPV($expectedResult, ...$args)
     {
         $result = Financial::NPV(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerNPV()
@@ -473,7 +473,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Financial::PRICE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerPRICE()
@@ -492,7 +492,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Financial::RATE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerRATE()
@@ -511,7 +511,7 @@ class FinancialTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = Financial::XIRR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerXIRR()
diff --git a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
index 371f2826..af611a74 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
@@ -15,49 +15,49 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testDUMMY()
     {
         $result = Functions::DUMMY();
-        $this->assertEquals('#Not Yet Implemented', $result);
+        self::assertEquals('#Not Yet Implemented', $result);
     }
 
     public function testDIV0()
     {
         $result = Functions::DIV0();
-        $this->assertEquals('#DIV/0!', $result);
+        self::assertEquals('#DIV/0!', $result);
     }
 
     public function testNA()
     {
         $result = Functions::NA();
-        $this->assertEquals('#N/A', $result);
+        self::assertEquals('#N/A', $result);
     }
 
     public function testNAN()
     {
         $result = Functions::NAN();
-        $this->assertEquals('#NUM!', $result);
+        self::assertEquals('#NUM!', $result);
     }
 
     public function testNAME()
     {
         $result = Functions::NAME();
-        $this->assertEquals('#NAME?', $result);
+        self::assertEquals('#NAME?', $result);
     }
 
     public function testREF()
     {
         $result = Functions::REF();
-        $this->assertEquals('#REF!', $result);
+        self::assertEquals('#REF!', $result);
     }
 
     public function testNULL()
     {
         $result = Functions::null();
-        $this->assertEquals('#NULL!', $result);
+        self::assertEquals('#NULL!', $result);
     }
 
     public function testVALUE()
     {
         $result = Functions::VALUE();
-        $this->assertEquals('#VALUE!', $result);
+        self::assertEquals('#VALUE!', $result);
     }
 
     /**
@@ -68,7 +68,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsBlank($expectedResult, ...$args)
     {
         $result = Functions::isBlank(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsBlank()
@@ -84,7 +84,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsErr($expectedResult, ...$args)
     {
         $result = Functions::isErr(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsErr()
@@ -100,7 +100,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsError($expectedResult, ...$args)
     {
         $result = Functions::isError(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsError()
@@ -116,7 +116,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testErrorType($expectedResult, ...$args)
     {
         $result = Functions::errorType(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerErrorType()
@@ -132,7 +132,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsLogical($expectedResult, ...$args)
     {
         $result = Functions::isLogical(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsLogical()
@@ -148,7 +148,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsNa($expectedResult, ...$args)
     {
         $result = Functions::isNa(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsNa()
@@ -164,7 +164,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsNumber($expectedResult, ...$args)
     {
         $result = Functions::isNumber(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsNumber()
@@ -180,7 +180,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsText($expectedResult, ...$args)
     {
         $result = Functions::isText(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsText()
@@ -196,7 +196,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsNonText($expectedResult, ...$args)
     {
         $result = Functions::isNonText(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsNonText()
@@ -212,7 +212,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsEven($expectedResult, ...$args)
     {
         $result = Functions::isEven(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsEven()
@@ -228,7 +228,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testIsOdd($expectedResult, ...$args)
     {
         $result = Functions::isOdd(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerIsOdd()
@@ -244,7 +244,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testTYPE($expectedResult, ...$args)
     {
         $result = Functions::TYPE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerTYPE()
@@ -260,7 +260,7 @@ class FunctionsTest extends PHPUnit_Framework_TestCase
     public function testN($expectedResult, ...$args)
     {
         $result = Functions::n(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerN()
diff --git a/tests/PhpSpreadsheetTests/Calculation/LogicalTest.php b/tests/PhpSpreadsheetTests/Calculation/LogicalTest.php
index d1aac26a..d9c70c2f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/LogicalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/LogicalTest.php
@@ -16,13 +16,13 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testTRUE()
     {
         $result = Logical::TRUE();
-        $this->assertTrue($result);
+        self::assertTrue($result);
     }
 
     public function testFALSE()
     {
         $result = Logical::FALSE();
-        $this->assertFalse($result);
+        self::assertFalse($result);
     }
 
     /**
@@ -33,7 +33,7 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testAND($expectedResult, ...$args)
     {
         $result = Logical::logicalAnd(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerAND()
@@ -49,7 +49,7 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testOR($expectedResult, ...$args)
     {
         $result = Logical::logicalOr(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerOR()
@@ -65,7 +65,7 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testNOT($expectedResult, ...$args)
     {
         $result = Logical::NOT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerNOT()
@@ -81,7 +81,7 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testIF($expectedResult, ...$args)
     {
         $result = Logical::statementIf(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerIF()
@@ -97,7 +97,7 @@ class LogicalTest extends PHPUnit_Framework_TestCase
     public function testIFERROR($expectedResult, ...$args)
     {
         $result = Logical::IFERROR(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerIFERROR()
diff --git a/tests/PhpSpreadsheetTests/Calculation/LookupRefTest.php b/tests/PhpSpreadsheetTests/Calculation/LookupRefTest.php
index 94696e4c..2671a529 100644
--- a/tests/PhpSpreadsheetTests/Calculation/LookupRefTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/LookupRefTest.php
@@ -25,7 +25,7 @@ class LookupRefTest extends PHPUnit_Framework_TestCase
     public function testHLOOKUP($expectedResult, ...$args)
     {
         $result = LookupRef::HLOOKUP(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerHLOOKUP()
@@ -42,7 +42,7 @@ class LookupRefTest extends PHPUnit_Framework_TestCase
     public function testVLOOKUP($expectedResult, ...$args)
     {
         $result = LookupRef::VLOOKUP(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerVLOOKUP()
@@ -59,7 +59,7 @@ class LookupRefTest extends PHPUnit_Framework_TestCase
     public function testMATCH($expectedResult, ...$args)
     {
         $result = LookupRef::MATCH(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerMATCH()
diff --git a/tests/PhpSpreadsheetTests/Calculation/MathTrigTest.php b/tests/PhpSpreadsheetTests/Calculation/MathTrigTest.php
index d765931c..29b9b57c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/MathTrigTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/MathTrigTest.php
@@ -22,7 +22,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testATAN2($expectedResult, ...$args)
     {
         $result = MathTrig::ATAN2(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerATAN2()
@@ -38,7 +38,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testCEILING($expectedResult, ...$args)
     {
         $result = MathTrig::CEILING(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerCEILING()
@@ -54,7 +54,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testCOMBIN($expectedResult, ...$args)
     {
         $result = MathTrig::COMBIN(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerCOMBIN()
@@ -70,7 +70,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testEVEN($expectedResult, ...$args)
     {
         $result = MathTrig::EVEN(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerEVEN()
@@ -86,7 +86,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testODD($expectedResult, ...$args)
     {
         $result = MathTrig::ODD(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerODD()
@@ -102,7 +102,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testFACT($expectedResult, ...$args)
     {
         $result = MathTrig::FACT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerFACT()
@@ -118,7 +118,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testFACTDOUBLE($expectedResult, ...$args)
     {
         $result = MathTrig::FACTDOUBLE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerFACTDOUBLE()
@@ -134,7 +134,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testFLOOR($expectedResult, ...$args)
     {
         $result = MathTrig::FLOOR(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerFLOOR()
@@ -150,7 +150,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testGCD($expectedResult, ...$args)
     {
         $result = MathTrig::GCD(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerGCD()
@@ -166,7 +166,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testLCM($expectedResult, ...$args)
     {
         $result = MathTrig::LCM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerLCM()
@@ -182,7 +182,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testINT($expectedResult, ...$args)
     {
         $result = MathTrig::INT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerINT()
@@ -198,7 +198,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testSIGN($expectedResult, ...$args)
     {
         $result = MathTrig::SIGN(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerSIGN()
@@ -214,7 +214,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testPOWER($expectedResult, ...$args)
     {
         $result = MathTrig::POWER(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerPOWER()
@@ -230,7 +230,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testLOG($expectedResult, ...$args)
     {
         $result = MathTrig::logBase(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerLOG()
@@ -246,7 +246,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testMOD($expectedResult, ...$args)
     {
         $result = MathTrig::MOD(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMOD()
@@ -262,7 +262,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testMDETERM($expectedResult, ...$args)
     {
         $result = MathTrig::MDETERM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMDETERM()
@@ -281,7 +281,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = MathTrig::MINVERSE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMINVERSE()
@@ -300,7 +300,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
         $this->markTestIncomplete('TODO: This test should be fixed');
 
         $result = MathTrig::MMULT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMMULT()
@@ -316,7 +316,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testMULTINOMIAL($expectedResult, ...$args)
     {
         $result = MathTrig::MULTINOMIAL(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMULTINOMIAL()
@@ -334,7 +334,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
         Calculation::setArrayReturnType(Calculation::RETURN_ARRAY_AS_VALUE);
         $result = MathTrig::MROUND(...$args);
         Calculation::setArrayReturnType(Calculation::RETURN_ARRAY_AS_ARRAY);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerMROUND()
@@ -350,7 +350,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testPRODUCT($expectedResult, ...$args)
     {
         $result = MathTrig::PRODUCT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerPRODUCT()
@@ -366,7 +366,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testQUOTIENT($expectedResult, ...$args)
     {
         $result = MathTrig::QUOTIENT(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerQUOTIENT()
@@ -382,7 +382,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testROUNDUP($expectedResult, ...$args)
     {
         $result = MathTrig::ROUNDUP(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerROUNDUP()
@@ -398,7 +398,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testROUNDDOWN($expectedResult, ...$args)
     {
         $result = MathTrig::ROUNDDOWN(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerROUNDDOWN()
@@ -414,7 +414,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testSERIESSUM($expectedResult, ...$args)
     {
         $result = MathTrig::SERIESSUM(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerSERIESSUM()
@@ -430,7 +430,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testSUMSQ($expectedResult, ...$args)
     {
         $result = MathTrig::SUMSQ(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerSUMSQ()
@@ -446,7 +446,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testTRUNC($expectedResult, ...$args)
     {
         $result = MathTrig::TRUNC(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerTRUNC()
@@ -462,7 +462,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testROMAN($expectedResult, ...$args)
     {
         $result = MathTrig::ROMAN(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerROMAN()
@@ -478,7 +478,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testSQRTPI($expectedResult, ...$args)
     {
         $result = MathTrig::SQRTPI(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerSQRTPI()
@@ -494,7 +494,7 @@ class MathTrigTest extends PHPUnit_Framework_TestCase
     public function testSUMIF($expectedResult, ...$args)
     {
         $result = MathTrig::SUMIF(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-12);
+        self::assertEquals($expectedResult, $result, null, 1E-12);
     }
 
     public function providerSUMIF()
diff --git a/tests/PhpSpreadsheetTests/Calculation/TextDataTest.php b/tests/PhpSpreadsheetTests/Calculation/TextDataTest.php
index 8a6cd0c5..84188689 100644
--- a/tests/PhpSpreadsheetTests/Calculation/TextDataTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/TextDataTest.php
@@ -22,7 +22,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testCHAR($expectedResult, ...$args)
     {
         $result = TextData::CHARACTER(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCHAR()
@@ -38,7 +38,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testCODE($expectedResult, ...$args)
     {
         $result = TextData::ASCIICODE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCODE()
@@ -54,7 +54,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testCONCATENATE($expectedResult, ...$args)
     {
         $result = TextData::CONCATENATE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCONCATENATE()
@@ -70,7 +70,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testLEFT($expectedResult, ...$args)
     {
         $result = TextData::LEFT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerLEFT()
@@ -86,7 +86,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testMID($expectedResult, ...$args)
     {
         $result = TextData::MID(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerMID()
@@ -102,7 +102,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testRIGHT($expectedResult, ...$args)
     {
         $result = TextData::RIGHT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerRIGHT()
@@ -118,7 +118,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testLOWER($expectedResult, ...$args)
     {
         $result = TextData::LOWERCASE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerLOWER()
@@ -134,7 +134,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testUPPER($expectedResult, ...$args)
     {
         $result = TextData::UPPERCASE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerUPPER()
@@ -150,7 +150,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testPROPER($expectedResult, ...$args)
     {
         $result = TextData::PROPERCASE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerPROPER()
@@ -166,7 +166,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testLEN($expectedResult, ...$args)
     {
         $result = TextData::STRINGLENGTH(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerLEN()
@@ -182,7 +182,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testSEARCH($expectedResult, ...$args)
     {
         $result = TextData::SEARCHINSENSITIVE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerSEARCH()
@@ -198,7 +198,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testFIND($expectedResult, ...$args)
     {
         $result = TextData::SEARCHSENSITIVE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerFIND()
@@ -214,7 +214,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testREPLACE($expectedResult, ...$args)
     {
         $result = TextData::REPLACE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerREPLACE()
@@ -230,7 +230,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testSUBSTITUTE($expectedResult, ...$args)
     {
         $result = TextData::SUBSTITUTE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerSUBSTITUTE()
@@ -246,7 +246,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testTRIM($expectedResult, ...$args)
     {
         $result = TextData::TRIMSPACES(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerTRIM()
@@ -262,7 +262,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testCLEAN($expectedResult, ...$args)
     {
         $result = TextData::TRIMNONPRINTABLE(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCLEAN()
@@ -278,7 +278,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testDOLLAR($expectedResult, ...$args)
     {
         $result = TextData::DOLLAR(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerDOLLAR()
@@ -294,7 +294,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testFIXED($expectedResult, ...$args)
     {
         $result = TextData::FIXEDFORMAT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerFIXED()
@@ -310,7 +310,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
     public function testT($expectedResult, ...$args)
     {
         $result = TextData::RETURNSTRING(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerT()
@@ -331,7 +331,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
         StringHelper::setCurrencyCode('$');
 
         $result = TextData::TEXTFORMAT(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerTEXT()
@@ -351,7 +351,7 @@ class TextDataTest extends PHPUnit_Framework_TestCase
         StringHelper::setCurrencyCode('$');
 
         $result = TextData::VALUE(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-8);
+        self::assertEquals($expectedResult, $result, null, 1E-8);
     }
 
     public function providerVALUE()
diff --git a/tests/PhpSpreadsheetTests/CalculationTest.php b/tests/PhpSpreadsheetTests/CalculationTest.php
index d8979979..3d89b9a0 100644
--- a/tests/PhpSpreadsheetTests/CalculationTest.php
+++ b/tests/PhpSpreadsheetTests/CalculationTest.php
@@ -24,11 +24,11 @@ class CalculationTest extends PHPUnit_Framework_TestCase
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
         $resultExcel = Calculation::getInstance()->_calculateFormulaValue($formula);
-        $this->assertEquals($expectedResultExcel, $resultExcel, 'should be Excel compatible');
+        self::assertEquals($expectedResultExcel, $resultExcel, 'should be Excel compatible');
 
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
         $resultOpenOffice = Calculation::getInstance()->_calculateFormulaValue($formula);
-        $this->assertEquals($expectedResultOpenOffice, $resultOpenOffice, 'should be OpenOffice compatible');
+        self::assertEquals($expectedResultOpenOffice, $resultOpenOffice, 'should be OpenOffice compatible');
     }
 
     public function providerBinaryComparisonOperation()
@@ -45,7 +45,7 @@ class CalculationTest extends PHPUnit_Framework_TestCase
      */
     public function testGetFunctions($category, $functionCall, $argumentCount)
     {
-        $this->assertInternalType('callable', $functionCall);
+        self::assertInternalType('callable', $functionCall);
     }
 
     public function providerGetFunctions()
@@ -56,10 +56,10 @@ class CalculationTest extends PHPUnit_Framework_TestCase
     public function testIsImplemented()
     {
         $calculation = Calculation::getInstance();
-        $this->assertFalse($calculation->isImplemented('non-existing-function'));
-        $this->assertFalse($calculation->isImplemented('AREAS'));
-        $this->assertTrue($calculation->isImplemented('coUNt'));
-        $this->assertTrue($calculation->isImplemented('abs'));
+        self::assertFalse($calculation->isImplemented('non-existing-function'));
+        self::assertFalse($calculation->isImplemented('AREAS'));
+        self::assertTrue($calculation->isImplemented('coUNt'));
+        self::assertTrue($calculation->isImplemented('abs'));
     }
 
     /**
@@ -70,7 +70,7 @@ class CalculationTest extends PHPUnit_Framework_TestCase
     public function testCanLoadAllSupportedLocales($locale)
     {
         $calculation = Calculation::getInstance();
-        $this->assertTrue($calculation->setLocale($locale));
+        self::assertTrue($calculation->setLocale($locale));
     }
 
     public function providerCanLoadAllSupportedLocales()
diff --git a/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php b/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
index 637ced24..f189d1ff 100644
--- a/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
@@ -74,6 +74,6 @@ class AdvancedValueBinderTest extends PHPUnit_Framework_TestCase
 
         $binder = new AdvancedValueBinder();
         $binder->bindValue($cell, $value);
-        $this->assertEquals($valueBinded, $cell->getValue());
+        self::assertEquals($valueBinded, $cell->getValue());
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php b/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
index 92ab1f29..e46820f3 100644
--- a/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
@@ -10,8 +10,8 @@ class DataTypeTest extends PHPUnit_Framework_TestCase
     public function testGetErrorCodes()
     {
         $result = DataType::getErrorCodes();
-        $this->assertInternalType('array', $result);
-        $this->assertGreaterThan(0, count($result));
-        $this->assertArrayHasKey('#NULL!', $result);
+        self::assertInternalType('array', $result);
+        self::assertGreaterThan(0, count($result));
+        self::assertArrayHasKey('#NULL!', $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php b/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
index 4d09a56a..0b74e075 100644
--- a/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
@@ -35,7 +35,7 @@ class DefaultValueBinderTest extends PHPUnit_Framework_TestCase
         $this->createCellStub();
         $binder = new DefaultValueBinder();
         $result = $binder->bindValue($this->cellStub, $value);
-        $this->assertTrue($result);
+        self::assertTrue($result);
     }
 
     public function binderProvider()
@@ -64,7 +64,7 @@ class DefaultValueBinderTest extends PHPUnit_Framework_TestCase
     public function testDataTypeForValue($expectedResult, ...$args)
     {
         $result = DefaultValueBinder::dataTypeForValue(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerDataTypeForValue()
@@ -79,6 +79,6 @@ class DefaultValueBinderTest extends PHPUnit_Framework_TestCase
 
         $expectedResult = DataType::TYPE_INLINE;
         $result = DefaultValueBinder::dataTypeForValue($objRichText);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php b/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
index 3d86cb62..419a8c91 100644
--- a/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
@@ -14,7 +14,7 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
         $testInstance = new Hyperlink($urlValue);
 
         $result = $testInstance->getUrl();
-        $this->assertEquals($urlValue, $result);
+        self::assertEquals($urlValue, $result);
     }
 
     public function testSetUrl()
@@ -24,10 +24,10 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
 
         $testInstance = new Hyperlink($initialUrlValue);
         $result = $testInstance->setUrl($newUrlValue);
-        $this->assertTrue($result instanceof Hyperlink);
+        self::assertTrue($result instanceof Hyperlink);
 
         $result = $testInstance->getUrl();
-        $this->assertEquals($newUrlValue, $result);
+        self::assertEquals($newUrlValue, $result);
     }
 
     public function testGetTooltip()
@@ -37,7 +37,7 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
         $testInstance = new Hyperlink(null, $tooltipValue);
 
         $result = $testInstance->getTooltip();
-        $this->assertEquals($tooltipValue, $result);
+        self::assertEquals($tooltipValue, $result);
     }
 
     public function testSetTooltip()
@@ -47,10 +47,10 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
 
         $testInstance = new Hyperlink(null, $initialTooltipValue);
         $result = $testInstance->setTooltip($newTooltipValue);
-        $this->assertTrue($result instanceof Hyperlink);
+        self::assertTrue($result instanceof Hyperlink);
 
         $result = $testInstance->getTooltip();
-        $this->assertEquals($newTooltipValue, $result);
+        self::assertEquals($newTooltipValue, $result);
     }
 
     public function testIsInternal()
@@ -60,11 +60,11 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
 
         $testInstance = new Hyperlink($initialUrlValue);
         $result = $testInstance->isInternal();
-        $this->assertFalse($result);
+        self::assertFalse($result);
 
         $testInstance->setUrl($newUrlValue);
         $result = $testInstance->isInternal();
-        $this->assertTrue($result);
+        self::assertTrue($result);
     }
 
     public function testGetHashCode()
@@ -76,6 +76,6 @@ class HyperlinkTest extends PHPUnit_Framework_TestCase
         $testInstance = new Hyperlink($urlValue, $tooltipValue);
 
         $result = $testInstance->getHashCode();
-        $this->assertEquals($initialExpectedHash, $result);
+        self::assertEquals($initialExpectedHash, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/CellTest.php b/tests/PhpSpreadsheetTests/CellTest.php
index 3a7d429e..6f03593a 100644
--- a/tests/PhpSpreadsheetTests/CellTest.php
+++ b/tests/PhpSpreadsheetTests/CellTest.php
@@ -16,7 +16,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testColumnIndexFromString($expectedResult, ...$args)
     {
         $result = Cell::columnIndexFromString(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColumnString()
@@ -30,8 +30,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::columnIndexFromString($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Column string index can not be longer than 3 characters');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Column string index can not be longer than 3 characters');
 
             return;
         }
@@ -44,8 +44,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::columnIndexFromString($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Column string index can not be empty');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Column string index can not be empty');
 
             return;
         }
@@ -60,7 +60,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testStringFromColumnIndex($expectedResult, ...$args)
     {
         $result = Cell::stringFromColumnIndex(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColumnIndex()
@@ -76,7 +76,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testCoordinateFromString($expectedResult, ...$args)
     {
         $result = Cell::coordinateFromString(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCoordinates()
@@ -90,8 +90,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::coordinateFromString($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
 
             return;
         }
@@ -104,8 +104,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::coordinateFromString($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Cell coordinate can not be zero-length string');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Cell coordinate can not be zero-length string');
 
             return;
         }
@@ -118,8 +118,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::coordinateFromString($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Invalid cell coordinate ' . $cellAddress);
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Invalid cell coordinate ' . $cellAddress);
 
             return;
         }
@@ -134,7 +134,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testAbsoluteCoordinateFromString($expectedResult, ...$args)
     {
         $result = Cell::absoluteCoordinate(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerAbsoluteCoordinates()
@@ -148,8 +148,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::absoluteCoordinate($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
 
             return;
         }
@@ -164,7 +164,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testAbsoluteReferenceFromString($expectedResult, ...$args)
     {
         $result = Cell::absoluteReference(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerAbsoluteReferences()
@@ -178,8 +178,8 @@ class CellTest extends PHPUnit_Framework_TestCase
         try {
             Cell::absoluteReference($cellAddress);
         } catch (\Exception $e) {
-            $this->assertInstanceOf(Exception::class, $e);
-            $this->assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
+            self::assertInstanceOf(Exception::class, $e);
+            self::assertEquals($e->getMessage(), 'Cell coordinate string can not be a range of cells');
 
             return;
         }
@@ -196,9 +196,9 @@ class CellTest extends PHPUnit_Framework_TestCase
         $result = Cell::splitRange(...$args);
         foreach ($result as $key => $split) {
             if (!is_array($expectedResult[$key])) {
-                $this->assertEquals($expectedResult[$key], $split[0]);
+                self::assertEquals($expectedResult[$key], $split[0]);
             } else {
-                $this->assertEquals($expectedResult[$key], $split);
+                self::assertEquals($expectedResult[$key], $split);
             }
         }
     }
@@ -216,7 +216,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testBuildRange($expectedResult, ...$args)
     {
         $result = Cell::buildRange(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerBuildRange()
@@ -245,7 +245,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testRangeBoundaries($expectedResult, ...$args)
     {
         $result = Cell::rangeBoundaries(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerRangeBoundaries()
@@ -261,7 +261,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testRangeDimension($expectedResult, ...$args)
     {
         $result = Cell::rangeDimension(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerRangeDimension()
@@ -277,7 +277,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testGetRangeBoundaries($expectedResult, ...$args)
     {
         $result = Cell::getRangeBoundaries(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerGetRangeBoundaries()
@@ -293,7 +293,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testExtractAllCellReferencesInRange($expectedResult, ...$args)
     {
         $result = Cell::extractAllCellReferencesInRange(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerExtractAllCellReferencesInRange()
@@ -309,7 +309,7 @@ class CellTest extends PHPUnit_Framework_TestCase
     public function testMergeRangesInCollection($expectedResult, ...$args)
     {
         $result = Cell::mergeRangesInCollection(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerMergeRangesInCollection()
diff --git a/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php b/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
index a7746b16..cdb46435 100644
--- a/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
@@ -19,7 +19,7 @@ class DataSeriesValuesTest extends PHPUnit_Framework_TestCase
 
         foreach ($dataTypeValues as $dataTypeValue) {
             $result = $testInstance->setDataType($dataTypeValue);
-            $this->assertTrue($result instanceof DataSeriesValues);
+            self::assertTrue($result instanceof DataSeriesValues);
         }
     }
 
@@ -30,7 +30,7 @@ class DataSeriesValuesTest extends PHPUnit_Framework_TestCase
         try {
             $testInstance->setDataType('BOOLEAN');
         } catch (Exception $e) {
-            $this->assertEquals($e->getMessage(), 'Invalid datatype for chart data series values');
+            self::assertEquals($e->getMessage(), 'Invalid datatype for chart data series values');
 
             return;
         }
@@ -45,6 +45,6 @@ class DataSeriesValuesTest extends PHPUnit_Framework_TestCase
         $testInstance->setDataType($dataTypeValue);
 
         $result = $testInstance->getDataType();
-        $this->assertEquals($dataTypeValue, $result);
+        self::assertEquals($dataTypeValue, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Chart/LayoutTest.php b/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
index 22daa18d..67cd5878 100644
--- a/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
@@ -14,7 +14,7 @@ class LayoutTest extends PHPUnit_Framework_TestCase
         $testInstance = new Layout();
 
         $result = $testInstance->setLayoutTarget($LayoutTargetValue);
-        $this->assertTrue($result instanceof Layout);
+        self::assertTrue($result instanceof Layout);
     }
 
     public function testGetLayoutTarget()
@@ -25,6 +25,6 @@ class LayoutTest extends PHPUnit_Framework_TestCase
         $setValue = $testInstance->setLayoutTarget($LayoutTargetValue);
 
         $result = $testInstance->getLayoutTarget();
-        $this->assertEquals($LayoutTargetValue, $result);
+        self::assertEquals($LayoutTargetValue, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Chart/LegendTest.php b/tests/PhpSpreadsheetTests/Chart/LegendTest.php
index 1df0ab70..82d3243b 100644
--- a/tests/PhpSpreadsheetTests/Chart/LegendTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LegendTest.php
@@ -21,7 +21,7 @@ class LegendTest extends PHPUnit_Framework_TestCase
 
         foreach ($positionValues as $positionValue) {
             $result = $testInstance->setPosition($positionValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -30,10 +30,10 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $testInstance = new Legend();
 
         $result = $testInstance->setPosition('BottomLeft');
-        $this->assertFalse($result);
+        self::assertFalse($result);
         //    Ensure that value is unchanged
         $result = $testInstance->getPosition();
-        $this->assertEquals(Legend::POSITION_RIGHT, $result);
+        self::assertEquals(Legend::POSITION_RIGHT, $result);
     }
 
     public function testGetPosition()
@@ -44,7 +44,7 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $setValue = $testInstance->setPosition($PositionValue);
 
         $result = $testInstance->getPosition();
-        $this->assertEquals($PositionValue, $result);
+        self::assertEquals($PositionValue, $result);
     }
 
     public function testSetPositionXL()
@@ -62,7 +62,7 @@ class LegendTest extends PHPUnit_Framework_TestCase
 
         foreach ($positionValues as $positionValue) {
             $result = $testInstance->setPositionXL($positionValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -71,10 +71,10 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $testInstance = new Legend();
 
         $result = $testInstance->setPositionXL(999);
-        $this->assertFalse($result);
+        self::assertFalse($result);
         //    Ensure that value is unchanged
         $result = $testInstance->getPositionXL();
-        $this->assertEquals(Legend::XL_LEGEND_POSITION_RIGHT, $result);
+        self::assertEquals(Legend::XL_LEGEND_POSITION_RIGHT, $result);
     }
 
     public function testGetPositionXL()
@@ -85,7 +85,7 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $setValue = $testInstance->setPositionXL($PositionValue);
 
         $result = $testInstance->getPositionXL();
-        $this->assertEquals($PositionValue, $result);
+        self::assertEquals($PositionValue, $result);
     }
 
     public function testSetOverlay()
@@ -99,7 +99,7 @@ class LegendTest extends PHPUnit_Framework_TestCase
 
         foreach ($overlayValues as $overlayValue) {
             $result = $testInstance->setOverlay($overlayValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -108,10 +108,10 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $testInstance = new Legend();
 
         $result = $testInstance->setOverlay('INVALID');
-        $this->assertFalse($result);
+        self::assertFalse($result);
 
         $result = $testInstance->getOverlay();
-        $this->assertFalse($result);
+        self::assertFalse($result);
     }
 
     public function testGetOverlay()
@@ -122,6 +122,6 @@ class LegendTest extends PHPUnit_Framework_TestCase
         $setValue = $testInstance->setOverlay($OverlayValue);
 
         $result = $testInstance->getOverlay();
-        $this->assertEquals($OverlayValue, $result);
+        self::assertEquals($OverlayValue, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Collection/CellsTest.php b/tests/PhpSpreadsheetTests/Collection/CellsTest.php
index 33899be7..a05107a2 100644
--- a/tests/PhpSpreadsheetTests/Collection/CellsTest.php
+++ b/tests/PhpSpreadsheetTests/Collection/CellsTest.php
@@ -18,49 +18,49 @@ class CellsTest extends PHPUnit_Framework_TestCase
         $collection = $sheet->getCellCollection();
 
         // Assert empty state
-        $this->assertEquals([], $collection->getCoordinates(), 'cell list should be empty');
-        $this->assertEquals([], $collection->getSortedCoordinates(), 'sorted cell list should be empty');
-        $this->assertNull($collection->get('B2'), 'getting non-existing cell must return null');
-        $this->assertFalse($collection->has('B2'), 'non-existing cell should be non-existent');
+        self::assertEquals([], $collection->getCoordinates(), 'cell list should be empty');
+        self::assertEquals([], $collection->getSortedCoordinates(), 'sorted cell list should be empty');
+        self::assertNull($collection->get('B2'), 'getting non-existing cell must return null');
+        self::assertFalse($collection->has('B2'), 'non-existing cell should be non-existent');
 
         // Add one cell
         $cell1 = $sheet->getCell('B2');
-        $this->assertSame($cell1, $collection->add('B2', $cell1), 'adding a cell should return the cell');
+        self::assertSame($cell1, $collection->add('B2', $cell1), 'adding a cell should return the cell');
 
         // Assert cell presence
-        $this->assertEquals(['B2'], $collection->getCoordinates(), 'cell list should contains the cell');
-        $this->assertEquals(['B2'], $collection->getSortedCoordinates(), 'sorted cell list contains the cell');
-        $this->assertSame($cell1, $collection->get('B2'), 'should get exact same object');
-        $this->assertTrue($collection->has('B2'), 'cell should exists');
+        self::assertEquals(['B2'], $collection->getCoordinates(), 'cell list should contains the cell');
+        self::assertEquals(['B2'], $collection->getSortedCoordinates(), 'sorted cell list contains the cell');
+        self::assertSame($cell1, $collection->get('B2'), 'should get exact same object');
+        self::assertTrue($collection->has('B2'), 'cell should exists');
 
         // Add a second cell
         $cell2 = $sheet->getCell('A1');
-        $this->assertSame($cell2, $collection->add('A1', $cell2), 'adding a second cell should return the cell');
-        $this->assertEquals(['B2', 'A1'], $collection->getCoordinates(), 'cell list should contains the cell');
-        $this->assertEquals(['A1', 'B2'], $collection->getSortedCoordinates(), 'sorted cell list contains the cell');
+        self::assertSame($cell2, $collection->add('A1', $cell2), 'adding a second cell should return the cell');
+        self::assertEquals(['B2', 'A1'], $collection->getCoordinates(), 'cell list should contains the cell');
+        self::assertEquals(['A1', 'B2'], $collection->getSortedCoordinates(), 'sorted cell list contains the cell');
 
         // Assert collection copy
         $sheet2 = $spreadsheet->createSheet();
         $collection2 = $collection->cloneCellCollection($sheet2);
-        $this->assertTrue($collection2->has('A1'));
+        self::assertTrue($collection2->has('A1'));
         $copiedCell2 = $collection2->get('A1');
-        $this->assertNotSame($cell2, $copiedCell2, 'copied cell should not be the same object any more');
-        $this->assertSame($collection2, $copiedCell2->getParent(), 'copied cell should be owned by the copied collection');
-        $this->assertSame('A1', $copiedCell2->getCoordinate(), 'copied cell should keep attributes');
+        self::assertNotSame($cell2, $copiedCell2, 'copied cell should not be the same object any more');
+        self::assertSame($collection2, $copiedCell2->getParent(), 'copied cell should be owned by the copied collection');
+        self::assertSame('A1', $copiedCell2->getCoordinate(), 'copied cell should keep attributes');
 
         // Assert deletion
         $collection->delete('B2');
-        $this->assertFalse($collection->has('B2'), 'cell should have been deleted');
-        $this->assertEquals(['A1'], $collection->getCoordinates(), 'cell list should contains the cell');
+        self::assertFalse($collection->has('B2'), 'cell should have been deleted');
+        self::assertEquals(['A1'], $collection->getCoordinates(), 'cell list should contains the cell');
 
         // Assert update
         $cell2 = $sheet->getCell('A1');
-        $this->assertSame($sheet->getCellCollection(), $collection);
-        $this->assertSame($cell2, $collection->update($cell2), 'should update existing cell');
+        self::assertSame($sheet->getCellCollection(), $collection);
+        self::assertSame($cell2, $collection->update($cell2), 'should update existing cell');
 
         $cell3 = $sheet->getCell('C3');
-        $this->assertSame($cell3, $collection->update($cell3), 'should silently add non-existing cell');
-        $this->assertEquals(['A1', 'C3'], $collection->getCoordinates(), 'cell list should contains the cell');
+        self::assertSame($cell3, $collection->update($cell3), 'should silently add non-existing cell');
+        self::assertEquals(['A1', 'C3'], $collection->getCoordinates(), 'cell list should contains the cell');
     }
 
     public function testCacheLastCell()
@@ -70,7 +70,7 @@ class CellsTest extends PHPUnit_Framework_TestCase
         $sheet = $workbook->getActiveSheet();
         $sheet->setCellValue('A1', 1);
         $sheet->setCellValue('A2', 2);
-        $this->assertEquals($cells, $sheet->getCoordinates(), 'list should include last added cell');
+        self::assertEquals($cells, $sheet->getCoordinates(), 'list should include last added cell');
     }
 
     public function testCanGetCellAfterAnotherIsDeleted()
@@ -82,7 +82,7 @@ class CellsTest extends PHPUnit_Framework_TestCase
         $sheet->setCellValue('A2', 1);
         $collection->delete('A1');
         $sheet->setCellValue('A3', 1);
-        $this->assertNotNull($collection->get('A2'), 'should be able to get back the cell even when another cell was deleted while this one was the current one');
+        self::assertNotNull($collection->get('A2'), 'should be able to get back the cell even when another cell was deleted while this one was the current one');
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Helper/MigratorTest.php b/tests/PhpSpreadsheetTests/Helper/MigratorTest.php
index cb91f65a..dace06fb 100644
--- a/tests/PhpSpreadsheetTests/Helper/MigratorTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/MigratorTest.php
@@ -13,7 +13,7 @@ class MigratorTest extends PHPUnit_Framework_TestCase
 
         foreach ($migrator->getMapping() as $classname) {
             if (substr_count($classname, '\\')) {
-                $this->assertTrue(class_exists($classname) || interface_exists($classname), 'mapping is wrong, class does not exists in project: ' . $classname);
+                self::assertTrue(class_exists($classname) || interface_exists($classname), 'mapping is wrong, class does not exists in project: ' . $classname);
             }
         }
     }
diff --git a/tests/PhpSpreadsheetTests/IOFactoryTest.php b/tests/PhpSpreadsheetTests/IOFactoryTest.php
index 071e4bb6..df1eb464 100644
--- a/tests/PhpSpreadsheetTests/IOFactoryTest.php
+++ b/tests/PhpSpreadsheetTests/IOFactoryTest.php
@@ -16,7 +16,7 @@ class IOFactoryTest extends PHPUnit_Framework_TestCase
     public function testIdentify($file, $expected)
     {
         $actual = IOFactory::identify($file);
-        $this->assertSame($expected, $actual);
+        self::assertSame($expected, $actual);
     }
 
     public function providerIdentify()
diff --git a/tests/PhpSpreadsheetTests/Reader/CsvTest.php b/tests/PhpSpreadsheetTests/Reader/CsvTest.php
index 90e94a52..14fddf07 100644
--- a/tests/PhpSpreadsheetTests/Reader/CsvTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/CsvTest.php
@@ -25,20 +25,20 @@ class CsvTest extends PHPUnit_Framework_TestCase
         $reader = new ReaderCsv();
         $reloadedSpreadsheet = $reader->load($filename);
         $actual = $reloadedSpreadsheet->getActiveSheet()->getCell('A1')->getCalculatedValue();
-        $this->assertSame($value, $actual, 'should be able to write and read strings with multiples quotes');
+        self::assertSame($value, $actual, 'should be able to write and read strings with multiples quotes');
     }
 
     public function testDelimiterDetection()
     {
         $reader = new ReaderCsv();
-        $this->assertNull($reader->getDelimiter());
+        self::assertNull($reader->getDelimiter());
 
         $filename = __DIR__ . '/../../data/Reader/CSV/semicolon_separated.csv';
         $spreadsheet = $reader->load($filename);
 
-        $this->assertSame(';', $reader->getDelimiter(), 'should be able to infer the delimiter');
+        self::assertSame(';', $reader->getDelimiter(), 'should be able to infer the delimiter');
 
         $actual = $spreadsheet->getActiveSheet()->getCell('C2')->getValue();
-        $this->assertSame('25,5', $actual, 'should be able to retrieve values with commas');
+        self::assertSame('25,5', $actual, 'should be able to retrieve values with commas');
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/HTMLTest.php b/tests/PhpSpreadsheetTests/Reader/HTMLTest.php
index ca85be9c..362d7fe6 100644
--- a/tests/PhpSpreadsheetTests/Reader/HTMLTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/HTMLTest.php
@@ -11,6 +11,6 @@ class HTMLTest extends PHPUnit_Framework_TestCase
     {
         $filename = __DIR__ . '/../../data/Reader/HTML/csv_with_angle_bracket.csv';
         $reader = new Html();
-        $this->assertFalse($reader->canRead($filename));
+        self::assertFalse($reader->canRead($filename));
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/OdsTest.php b/tests/PhpSpreadsheetTests/Reader/OdsTest.php
index 658869b0..5c997f70 100644
--- a/tests/PhpSpreadsheetTests/Reader/OdsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/OdsTest.php
@@ -64,7 +64,7 @@ class OdsTest extends PHPUnit_Framework_TestCase
 
         // Test "listWorksheetNames" method
 
-        $this->assertEquals([
+        self::assertEquals([
             'Sheet1',
             'Second Sheet',
         ], $reader->listWorksheetNames($filename));
@@ -74,15 +74,15 @@ class OdsTest extends PHPUnit_Framework_TestCase
     {
         $spreadsheet = $this->loadDataFile();
 
-        $this->assertInstanceOf('PhpOffice\PhpSpreadsheet\Spreadsheet', $spreadsheet);
+        self::assertInstanceOf('PhpOffice\PhpSpreadsheet\Spreadsheet', $spreadsheet);
 
-        $this->assertEquals(2, $spreadsheet->getSheetCount());
+        self::assertEquals(2, $spreadsheet->getSheetCount());
 
         $firstSheet = $spreadsheet->getSheet(0);
-        $this->assertInstanceOf('PhpOffice\PhpSpreadsheet\Worksheet', $firstSheet);
+        self::assertInstanceOf('PhpOffice\PhpSpreadsheet\Worksheet', $firstSheet);
 
         $secondSheet = $spreadsheet->getSheet(1);
-        $this->assertInstanceOf('PhpOffice\PhpSpreadsheet\Worksheet', $secondSheet);
+        self::assertInstanceOf('PhpOffice\PhpSpreadsheet\Worksheet', $secondSheet);
     }
 
     public function testReadValueAndComments()
@@ -91,45 +91,45 @@ class OdsTest extends PHPUnit_Framework_TestCase
 
         $firstSheet = $spreadsheet->getSheet(0);
 
-        $this->assertEquals(29, $firstSheet->getHighestRow());
-        $this->assertEquals('N', $firstSheet->getHighestColumn());
+        self::assertEquals(29, $firstSheet->getHighestRow());
+        self::assertEquals('N', $firstSheet->getHighestColumn());
 
         // Simple cell value
-        $this->assertEquals('Test String 1', $firstSheet->getCell('A1')->getValue());
+        self::assertEquals('Test String 1', $firstSheet->getCell('A1')->getValue());
 
         // Merged cell
-        $this->assertEquals('BOX', $firstSheet->getCell('B18')->getValue());
+        self::assertEquals('BOX', $firstSheet->getCell('B18')->getValue());
 
         // Comments/Annotations
-        $this->assertEquals(
+        self::assertEquals(
             'Test for a simple colour-formatted string',
             $firstSheet->getComment('A1')->getText()->getPlainText()
         );
 
         // Data types
-        $this->assertEquals(DataType::TYPE_STRING, $firstSheet->getCell('A1')->getDataType());
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('B1')->getDataType()); // Int
+        self::assertEquals(DataType::TYPE_STRING, $firstSheet->getCell('A1')->getDataType());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('B1')->getDataType()); // Int
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('B6')->getDataType()); // Float
-        $this->assertEquals(1.23, $firstSheet->getCell('B6')->getValue());
-        $this->assertEquals(0, $firstSheet->getCell('G10')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('B6')->getDataType()); // Float
+        self::assertEquals(1.23, $firstSheet->getCell('B6')->getValue());
+        self::assertEquals(0, $firstSheet->getCell('G10')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A10')->getDataType()); // Date
-        $this->assertEquals(22269.0, $firstSheet->getCell('A10')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A10')->getDataType()); // Date
+        self::assertEquals(22269.0, $firstSheet->getCell('A10')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A13')->getDataType()); // Time
-        $this->assertEquals(25569.0625, $firstSheet->getCell('A13')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A13')->getDataType()); // Time
+        self::assertEquals(25569.0625, $firstSheet->getCell('A13')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A15')->getDataType()); // Date + Time
-        $this->assertEquals(22269.0625, $firstSheet->getCell('A15')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A15')->getDataType()); // Date + Time
+        self::assertEquals(22269.0625, $firstSheet->getCell('A15')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A11')->getDataType()); // Fraction
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A11')->getDataType()); // Fraction
 
-        $this->assertEquals(DataType::TYPE_BOOL, $firstSheet->getCell('D6')->getDataType());
-        $this->assertTrue($firstSheet->getCell('D6')->getValue());
+        self::assertEquals(DataType::TYPE_BOOL, $firstSheet->getCell('D6')->getDataType());
+        self::assertTrue($firstSheet->getCell('D6')->getValue());
 
-        $this->assertEquals(DataType::TYPE_FORMULA, $firstSheet->getCell('C6')->getDataType()); // Formula
-        $this->assertEquals('=TRUE()', $firstSheet->getCell('C6')->getValue()); // Formula
+        self::assertEquals(DataType::TYPE_FORMULA, $firstSheet->getCell('C6')->getDataType()); // Formula
+        self::assertEquals('=TRUE()', $firstSheet->getCell('C6')->getValue()); // Formula
 
         /*
          * Percentage, Currency
@@ -139,17 +139,17 @@ class OdsTest extends PHPUnit_Framework_TestCase
 
         $firstSheet = $spreadsheet->getSheet(0);
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A1')->getDataType()); // Percentage (10%)
-        $this->assertEquals(0.1, $firstSheet->getCell('A1')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A1')->getDataType()); // Percentage (10%)
+        self::assertEquals(0.1, $firstSheet->getCell('A1')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A2')->getDataType()); // Percentage (10.00%)
-        $this->assertEquals(0.1, $firstSheet->getCell('A2')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A2')->getDataType()); // Percentage (10.00%)
+        self::assertEquals(0.1, $firstSheet->getCell('A2')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A4')->getDataType()); // Currency (€10.00)
-        $this->assertEquals(10, $firstSheet->getCell('A4')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A4')->getDataType()); // Currency (€10.00)
+        self::assertEquals(10, $firstSheet->getCell('A4')->getValue());
 
-        $this->assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A5')->getDataType()); // Currency ($20)
-        $this->assertEquals(20, $firstSheet->getCell('A5')->getValue());
+        self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A5')->getDataType()); // Currency ($20)
+        self::assertEquals(20, $firstSheet->getCell('A5')->getValue());
     }
 
     public function testReadColors()
@@ -161,9 +161,9 @@ class OdsTest extends PHPUnit_Framework_TestCase
 
         $style = $firstSheet->getCell('K3')->getStyle();
 
-        $this->assertEquals('none', $style->getFill()->getFillType());
-        $this->assertEquals('FFFFFFFF', $style->getFill()->getStartColor()->getARGB());
-        $this->assertEquals('FF000000', $style->getFill()->getEndColor()->getARGB());
+        self::assertEquals('none', $style->getFill()->getFillType());
+        self::assertEquals('FFFFFFFF', $style->getFill()->getStartColor()->getARGB());
+        self::assertEquals('FF000000', $style->getFill()->getEndColor()->getARGB());
     }
 
     public function testReadRichText()
@@ -171,7 +171,7 @@ class OdsTest extends PHPUnit_Framework_TestCase
         $spreadsheet = $this->loadOOCalcTestFile();
         $firstSheet = $spreadsheet->getSheet(0);
 
-        $this->assertEquals(
+        self::assertEquals(
             "I don't know if OOCalc supports Rich Text in the same way as Excel, " .
             'And this row should be autofit height with text wrap',
             $firstSheet->getCell('A28')->getValue()
@@ -183,10 +183,10 @@ class OdsTest extends PHPUnit_Framework_TestCase
         $spreadsheet = $this->loadDataFile();
         $firstSheet = $spreadsheet->getSheet(0);
 
-        $this->assertEquals('This has    4 spaces before and 2 after  ', $firstSheet->getCell('A8')->getValue());
-        $this->assertEquals('This only one after ', $firstSheet->getCell('A9')->getValue());
-        $this->assertEquals('Test with DIFFERENT styles     and multiple spaces:  ', $firstSheet->getCell('A10')->getValue());
-        $this->assertEquals("test with new \nLines", $firstSheet->getCell('A11')->getValue());
+        self::assertEquals('This has    4 spaces before and 2 after  ', $firstSheet->getCell('A8')->getValue());
+        self::assertEquals('This only one after ', $firstSheet->getCell('A9')->getValue());
+        self::assertEquals('Test with DIFFERENT styles     and multiple spaces:  ', $firstSheet->getCell('A10')->getValue());
+        self::assertEquals("test with new \nLines", $firstSheet->getCell('A11')->getValue());
     }
 
     public function testReadHyperlinks()
@@ -196,9 +196,9 @@ class OdsTest extends PHPUnit_Framework_TestCase
 
         $hyperlink = $firstSheet->getCell('A29');
 
-        $this->assertEquals(DataType::TYPE_STRING, $hyperlink->getDataType());
-        $this->assertEquals('PHPExcel', $hyperlink->getValue());
-        $this->assertEquals('http://www.phpexcel.net/', $hyperlink->getHyperlink()->getUrl());
+        self::assertEquals(DataType::TYPE_STRING, $hyperlink->getDataType());
+        self::assertEquals('PHPExcel', $hyperlink->getValue());
+        self::assertEquals('http://www.phpexcel.net/', $hyperlink->getHyperlink()->getUrl());
     }
 
     /*
@@ -215,15 +215,15 @@ class OdsTest extends PHPUnit_Framework_TestCase
         // Font styles
 
         $style = $firstSheet->getCell('A1')->getStyle();
-        $this->assertEquals('FF000000', $style->getFont()->getColor()->getARGB());
-        $this->assertEquals(11, $style->getFont()->getSize());
-        $this->assertEquals(Font::UNDERLINE_NONE, $style->getFont()->getUnderline());
+        self::assertEquals('FF000000', $style->getFont()->getColor()->getARGB());
+        self::assertEquals(11, $style->getFont()->getSize());
+        self::assertEquals(Font::UNDERLINE_NONE, $style->getFont()->getUnderline());
 
         $style = $firstSheet->getCell('E3')->getStyle();
-        $this->assertEquals(Font::UNDERLINE_SINGLE, $style->getFont()->getUnderline());
+        self::assertEquals(Font::UNDERLINE_SINGLE, $style->getFont()->getUnderline());
 
         $style = $firstSheet->getCell('E1')->getStyle();
-        $this->assertTrue($style->getFont()->getBold());
-        $this->assertTrue($style->getFont()->getItalic());
+        self::assertTrue($style->getFont()->getBold());
+        self::assertTrue($style->getFont()->getItalic());
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/XEEValidatorTest.php b/tests/PhpSpreadsheetTests/Reader/XEEValidatorTest.php
index 13ca9576..7b2ff48a 100644
--- a/tests/PhpSpreadsheetTests/Reader/XEEValidatorTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/XEEValidatorTest.php
@@ -20,7 +20,7 @@ class XEEValidatorTest extends PHPUnit_Framework_TestCase
         $reader = $this->getMockForAbstractClass(BaseReader::class);
         $expectedResult = 'FAILURE: Should throw an Exception rather than return a value';
         $result = $reader->securityScanFile($filename);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerInvalidXML()
@@ -65,7 +65,7 @@ class XEEValidatorTest extends PHPUnit_Framework_TestCase
     {
         $reader = $this->getMockForAbstractClass(BaseReader::class);
         $result = $reader->securityScanFile($filename);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerValidXML()
diff --git a/tests/PhpSpreadsheetTests/ReferenceHelperTest.php b/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
index 1f7e0d56..e25f072f 100644
--- a/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
+++ b/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
@@ -28,7 +28,7 @@ class ReferenceHelperTest extends PHPUnit_Framework_TestCase
         shuffle($columnBase);
         usort($columnBase, [ReferenceHelper::class, 'columnSort']);
         foreach ($columnBase as $key => $value) {
-            $this->assertEquals($columnExpectedResult[$key], $value);
+            self::assertEquals($columnExpectedResult[$key], $value);
         }
     }
 
@@ -50,7 +50,7 @@ class ReferenceHelperTest extends PHPUnit_Framework_TestCase
         $columnExpectedResult = array_reverse($columnExpectedResult);
         usort($columnBase, [ReferenceHelper::class, 'columnReverseSort']);
         foreach ($columnBase as $key => $value) {
-            $this->assertEquals($columnExpectedResult[$key], $value);
+            self::assertEquals($columnExpectedResult[$key], $value);
         }
     }
 }
diff --git a/tests/PhpSpreadsheetTests/SettingsTest.php b/tests/PhpSpreadsheetTests/SettingsTest.php
index ec0e12ea..2abbe1b4 100644
--- a/tests/PhpSpreadsheetTests/SettingsTest.php
+++ b/tests/PhpSpreadsheetTests/SettingsTest.php
@@ -26,15 +26,15 @@ class SettingsTest extends PHPUnit_Framework_TestCase
     public function testGetXMLSettings()
     {
         $result = Settings::getLibXmlLoaderOptions();
-        $this->assertTrue((bool) ((LIBXML_DTDLOAD | LIBXML_DTDATTR) & $result));
-        $this->assertFalse(libxml_disable_entity_loader());
+        self::assertTrue((bool) ((LIBXML_DTDLOAD | LIBXML_DTDATTR) & $result));
+        self::assertFalse(libxml_disable_entity_loader());
     }
 
     public function testSetXMLSettings()
     {
         Settings::setLibXmlLoaderOptions(LIBXML_DTDLOAD | LIBXML_DTDATTR | LIBXML_DTDVALID);
         $result = Settings::getLibXmlLoaderOptions();
-        $this->assertTrue((bool) ((LIBXML_DTDLOAD | LIBXML_DTDATTR | LIBXML_DTDVALID) & $result));
-        $this->assertFalse(libxml_disable_entity_loader());
+        self::assertTrue((bool) ((LIBXML_DTDLOAD | LIBXML_DTDATTR | LIBXML_DTDVALID) & $result));
+        self::assertFalse(libxml_disable_entity_loader());
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Shared/CodePageTest.php b/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
index 7841fe98..77009581 100644
--- a/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
@@ -16,7 +16,7 @@ class CodePageTest extends PHPUnit_Framework_TestCase
     public function testCodePageNumberToName($expectedResult, ...$args)
     {
         $result = CodePage::numberToName(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCodePage()
@@ -30,7 +30,7 @@ class CodePageTest extends PHPUnit_Framework_TestCase
         try {
             CodePage::numberToName($invalidCodePage);
         } catch (Exception $e) {
-            $this->assertEquals($e->getMessage(), 'Unknown codepage: 12345');
+            self::assertEquals($e->getMessage(), 'Unknown codepage: 12345');
 
             return;
         }
@@ -43,7 +43,7 @@ class CodePageTest extends PHPUnit_Framework_TestCase
         try {
             CodePage::numberToName($unsupportedCodePage);
         } catch (Exception $e) {
-            $this->assertEquals($e->getMessage(), 'Code page 720 not supported.');
+            self::assertEquals($e->getMessage(), 'Code page 720 not supported.');
 
             return;
         }
diff --git a/tests/PhpSpreadsheetTests/Shared/DateTest.php b/tests/PhpSpreadsheetTests/Shared/DateTest.php
index 2e6d028d..f6b71b02 100644
--- a/tests/PhpSpreadsheetTests/Shared/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/DateTest.php
@@ -16,7 +16,7 @@ class DateTest extends PHPUnit_Framework_TestCase
 
         foreach ($calendarValues as $calendarValue) {
             $result = Date::setExcelCalendar($calendarValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -24,7 +24,7 @@ class DateTest extends PHPUnit_Framework_TestCase
     {
         $unsupportedCalendar = '2012';
         $result = Date::setExcelCalendar($unsupportedCalendar);
-        $this->assertFalse($result);
+        self::assertFalse($result);
     }
 
     /**
@@ -37,7 +37,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
         $result = Date::excelToTimestamp(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerDateTimeExcelToTimestamp1900()
@@ -55,7 +55,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
         $result = Date::timestampToExcel(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-5);
+        self::assertEquals($expectedResult, $result, null, 1E-5);
     }
 
     public function providerDateTimeTimestampToExcel1900()
@@ -73,7 +73,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
         $result = Date::dateTimeToExcel(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-5);
+        self::assertEquals($expectedResult, $result, null, 1E-5);
     }
 
     public function providerDateTimeDateTimeToExcel()
@@ -91,7 +91,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
         $result = Date::formattedPHPToExcel(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-5);
+        self::assertEquals($expectedResult, $result, null, 1E-5);
     }
 
     public function providerDateTimeFormattedPHPToExcel1900()
@@ -109,7 +109,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
 
         $result = Date::excelToTimestamp(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerDateTimeExcelToTimestamp1904()
@@ -127,7 +127,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
 
         $result = Date::timestampToExcel(...$args);
-        $this->assertEquals($expectedResult, $result, null, 1E-5);
+        self::assertEquals($expectedResult, $result, null, 1E-5);
     }
 
     public function providerDateTimeTimestampToExcel1904()
@@ -143,7 +143,7 @@ class DateTest extends PHPUnit_Framework_TestCase
     public function testIsDateTimeFormatCode($expectedResult, ...$args)
     {
         $result = Date::isDateTimeFormatCode(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerIsDateTimeFormatCode()
@@ -161,7 +161,7 @@ class DateTest extends PHPUnit_Framework_TestCase
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
         $result = Date::excelToTimestamp(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerDateTimeExcelToTimestamp1900Timezone()
diff --git a/tests/PhpSpreadsheetTests/Shared/FileTest.php b/tests/PhpSpreadsheetTests/Shared/FileTest.php
index 5f148a2a..65e5959e 100644
--- a/tests/PhpSpreadsheetTests/Shared/FileTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/FileTest.php
@@ -12,7 +12,7 @@ class FileTest extends PHPUnit_Framework_TestCase
         $expectedResult = false;
 
         $result = File::getUseUploadTempDirectory();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetUseUploadTempDirectory()
@@ -26,7 +26,7 @@ class FileTest extends PHPUnit_Framework_TestCase
             File::setUseUploadTempDirectory($useUploadTempDirectoryValue);
 
             $result = File::getUseUploadTempDirectory();
-            $this->assertEquals($useUploadTempDirectoryValue, $result);
+            self::assertEquals($useUploadTempDirectoryValue, $result);
         }
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Shared/FontTest.php b/tests/PhpSpreadsheetTests/Shared/FontTest.php
index 76a40d1c..1f9f215e 100644
--- a/tests/PhpSpreadsheetTests/Shared/FontTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/FontTest.php
@@ -12,7 +12,7 @@ class FontTest extends PHPUnit_Framework_TestCase
         $expectedResult = Font::AUTOSIZE_METHOD_APPROX;
 
         $result = Font::getAutoSizeMethod();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetAutoSizeMethod()
@@ -24,7 +24,7 @@ class FontTest extends PHPUnit_Framework_TestCase
 
         foreach ($autosizeMethodValues as $autosizeMethodValue) {
             $result = Font::setAutoSizeMethod($autosizeMethodValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -33,7 +33,7 @@ class FontTest extends PHPUnit_Framework_TestCase
         $unsupportedAutosizeMethod = 'guess';
 
         $result = Font::setAutoSizeMethod($unsupportedAutosizeMethod);
-        $this->assertFalse($result);
+        self::assertFalse($result);
     }
 
     /**
@@ -44,7 +44,7 @@ class FontTest extends PHPUnit_Framework_TestCase
     public function testFontSizeToPixels($expectedResult, ...$args)
     {
         $result = Font::fontSizeToPixels(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerFontSizeToPixels()
@@ -60,7 +60,7 @@ class FontTest extends PHPUnit_Framework_TestCase
     public function testInchSizeToPixels($expectedResult, ...$args)
     {
         $result = Font::inchSizeToPixels(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerInchSizeToPixels()
@@ -76,7 +76,7 @@ class FontTest extends PHPUnit_Framework_TestCase
     public function testCentimeterSizeToPixels($expectedResult, ...$args)
     {
         $result = Font::centimeterSizeToPixels(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerCentimeterSizeToPixels()
diff --git a/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php b/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
index 271deefc..880159df 100644
--- a/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
@@ -16,7 +16,7 @@ class PasswordHasherTest extends PHPUnit_Framework_TestCase
     public function testHashPassword($expectedResult, ...$args)
     {
         $result = PasswordHasher::hashPassword(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerHashPassword()
diff --git a/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php b/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
index 67b82f7e..64e584d9 100644
--- a/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
@@ -18,7 +18,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
     public function testGetIsIconvEnabled()
     {
         $result = StringHelper::getIsIconvEnabled();
-        $this->assertTrue($result);
+        self::assertTrue($result);
     }
 
     public function testGetDecimalSeparator()
@@ -27,7 +27,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
 
         $expectedResult = (!empty($localeconv['decimal_point'])) ? $localeconv['decimal_point'] : ',';
         $result = StringHelper::getDecimalSeparator();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetDecimalSeparator()
@@ -36,7 +36,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         StringHelper::setDecimalSeparator($expectedResult);
 
         $result = StringHelper::getDecimalSeparator();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetThousandsSeparator()
@@ -45,7 +45,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
 
         $expectedResult = (!empty($localeconv['thousands_sep'])) ? $localeconv['thousands_sep'] : ',';
         $result = StringHelper::getThousandsSeparator();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetThousandsSeparator()
@@ -54,7 +54,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         StringHelper::setThousandsSeparator($expectedResult);
 
         $result = StringHelper::getThousandsSeparator();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetCurrencyCode()
@@ -62,7 +62,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         $localeconv = localeconv();
         $expectedResult = (!empty($localeconv['currency_symbol']) ? $localeconv['currency_symbol'] : (!empty($localeconv['int_curr_symbol']) ? $localeconv['int_curr_symbol'] : '$'));
         $result = StringHelper::getCurrencyCode();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetCurrencyCode()
@@ -71,7 +71,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         StringHelper::setCurrencyCode($expectedResult);
 
         $result = StringHelper::getCurrencyCode();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testControlCharacterPHP2OOXML()
@@ -79,7 +79,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         $expectedResult = 'foo_x000B_bar';
         $result = StringHelper::controlCharacterPHP2OOXML('foo' . chr(11) . 'bar');
 
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testControlCharacterOOXML2PHP()
@@ -87,7 +87,7 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         $expectedResult = 'foo' . chr(11) . 'bar';
         $result = StringHelper::controlCharacterOOXML2PHP('foo_x000B_bar');
 
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSYLKtoUTF8()
@@ -95,6 +95,6 @@ class StringHelperTest extends PHPUnit_Framework_TestCase
         $expectedResult = 'foo' . chr(11) . 'bar';
         $result = StringHelper::SYLKtoUTF8("foo\x1B ;bar");
 
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php b/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
index 706955c2..ddddade6 100644
--- a/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
@@ -19,7 +19,7 @@ class TimeZoneTest extends PHPUnit_Framework_TestCase
 
         foreach ($timezoneValues as $timezoneValue) {
             $result = TimeZone::setTimezone($timezoneValue);
-            $this->assertTrue($result);
+            self::assertTrue($result);
         }
     }
 
@@ -27,6 +27,6 @@ class TimeZoneTest extends PHPUnit_Framework_TestCase
     {
         $unsupportedTimezone = 'Etc/GMT+10';
         $result = TimeZone::setTimezone($unsupportedTimezone);
-        $this->assertFalse($result);
+        self::assertFalse($result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Style/BorderTest.php b/tests/PhpSpreadsheetTests/Style/BorderTest.php
index 4055c870..7f772e90 100644
--- a/tests/PhpSpreadsheetTests/Style/BorderTest.php
+++ b/tests/PhpSpreadsheetTests/Style/BorderTest.php
@@ -16,11 +16,11 @@ class BorderTest extends PHPUnit_Framework_TestCase
         $bottom = $borders->getBottom();
 
         $actual = $bottom->getBorderStyle();
-        $this->assertSame(Border::BORDER_NONE, $actual, 'should default to none');
+        self::assertSame(Border::BORDER_NONE, $actual, 'should default to none');
 
         $allBorders->setBorderStyle(Border::BORDER_THIN);
 
         $actual = $bottom->getBorderStyle();
-        $this->assertSame(Border::BORDER_THIN, $actual, 'should have been set via allBorders');
+        self::assertSame(Border::BORDER_THIN, $actual, 'should have been set via allBorders');
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Style/ColorTest.php b/tests/PhpSpreadsheetTests/Style/ColorTest.php
index 6ed161d2..26ff0f6f 100644
--- a/tests/PhpSpreadsheetTests/Style/ColorTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ColorTest.php
@@ -15,7 +15,7 @@ class ColorTest extends PHPUnit_Framework_TestCase
     public function testGetRed($expectedResult, ...$args)
     {
         $result = Color::getRed(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColorGetRed()
@@ -31,7 +31,7 @@ class ColorTest extends PHPUnit_Framework_TestCase
     public function testGetGreen($expectedResult, ...$args)
     {
         $result = Color::getGreen(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColorGetGreen()
@@ -47,7 +47,7 @@ class ColorTest extends PHPUnit_Framework_TestCase
     public function testGetBlue($expectedResult, ...$args)
     {
         $result = Color::getBlue(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColorGetBlue()
@@ -63,7 +63,7 @@ class ColorTest extends PHPUnit_Framework_TestCase
     public function testChangeBrightness($expectedResult, ...$args)
     {
         $result = Color::changeBrightness(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerColorChangeBrightness()
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatDateTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatDateTest.php
index af462e41..c9cc3d00 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormatDateTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatDateTest.php
@@ -22,7 +22,7 @@ class NumberFormatDateTest extends PHPUnit_Framework_TestCase
     public function testFormatValueWithMask($expectedResult, ...$args)
     {
         $result = NumberFormat::toFormattedString(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerNumberFormat()
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
index 72c7fbe4..f0b5647a 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
@@ -22,7 +22,7 @@ class NumberFormatTest extends PHPUnit_Framework_TestCase
     public function testFormatValueWithMask($expectedResult, ...$args)
     {
         $result = NumberFormat::toFormattedString(...$args);
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function providerNumberFormat()
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/Column/RuleTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/Column/RuleTest.php
index b7760e25..a93ed360 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/Column/RuleTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/Column/RuleTest.php
@@ -24,7 +24,7 @@ class RuleTest extends PHPUnit_Framework_TestCase
     public function testGetRuleType()
     {
         $result = $this->testAutoFilterRuleObject->getRuleType();
-        $this->assertEquals(Column\Rule::AUTOFILTER_RULETYPE_FILTER, $result);
+        self::assertEquals(Column\Rule::AUTOFILTER_RULETYPE_FILTER, $result);
     }
 
     public function testSetRuleType()
@@ -33,10 +33,10 @@ class RuleTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterRuleObject->setRuleType($expectedResult);
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
 
         $result = $this->testAutoFilterRuleObject->getRuleType();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetValue()
@@ -45,16 +45,16 @@ class RuleTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterRuleObject->setValue($expectedResult);
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
 
         $result = $this->testAutoFilterRuleObject->getValue();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetOperator()
     {
         $result = $this->testAutoFilterRuleObject->getOperator();
-        $this->assertEquals(Column\Rule::AUTOFILTER_COLUMN_RULE_EQUAL, $result);
+        self::assertEquals(Column\Rule::AUTOFILTER_COLUMN_RULE_EQUAL, $result);
     }
 
     public function testSetOperator()
@@ -63,10 +63,10 @@ class RuleTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterRuleObject->setOperator($expectedResult);
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
 
         $result = $this->testAutoFilterRuleObject->getOperator();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetGrouping()
@@ -75,28 +75,28 @@ class RuleTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterRuleObject->setGrouping($expectedResult);
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
 
         $result = $this->testAutoFilterRuleObject->getGrouping();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetParent()
     {
         $result = $this->testAutoFilterRuleObject->getParent();
-        $this->assertInstanceOf(Column::class, $result);
+        self::assertInstanceOf(Column::class, $result);
     }
 
     public function testSetParent()
     {
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterRuleObject->setParent($this->mockAutoFilterColumnObject);
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
     }
 
     public function testClone()
     {
         $result = clone $this->testAutoFilterRuleObject;
-        $this->assertInstanceOf(Column\Rule::class, $result);
+        self::assertInstanceOf(Column\Rule::class, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
index e171e814..cf9944fc 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
@@ -27,7 +27,7 @@ class ColumnTest extends PHPUnit_Framework_TestCase
     public function testGetColumnIndex()
     {
         $result = $this->testAutoFilterColumnObject->getColumnIndex();
-        $this->assertEquals($this->testInitialColumn, $result);
+        self::assertEquals($this->testInitialColumn, $result);
     }
 
     public function testSetColumnIndex()
@@ -36,38 +36,38 @@ class ColumnTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterColumnObject->setColumnIndex($expectedResult);
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
 
         $result = $this->testAutoFilterColumnObject->getColumnIndex();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetParent()
     {
         $result = $this->testAutoFilterColumnObject->getParent();
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
     }
 
     public function testSetParent()
     {
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterColumnObject->setParent($this->mockAutoFilterObject);
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
     }
 
     public function testGetFilterType()
     {
         $result = $this->testAutoFilterColumnObject->getFilterType();
-        $this->assertEquals(AutoFilter\Column::AUTOFILTER_FILTERTYPE_FILTER, $result);
+        self::assertEquals(AutoFilter\Column::AUTOFILTER_FILTERTYPE_FILTER, $result);
     }
 
     public function testSetFilterType()
     {
         $result = $this->testAutoFilterColumnObject->setFilterType(AutoFilter\Column::AUTOFILTER_FILTERTYPE_DYNAMICFILTER);
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
 
         $result = $this->testAutoFilterColumnObject->getFilterType();
-        $this->assertEquals(AutoFilter\Column::AUTOFILTER_FILTERTYPE_DYNAMICFILTER, $result);
+        self::assertEquals(AutoFilter\Column::AUTOFILTER_FILTERTYPE_DYNAMICFILTER, $result);
     }
 
     /**
@@ -83,16 +83,16 @@ class ColumnTest extends PHPUnit_Framework_TestCase
     public function testGetJoin()
     {
         $result = $this->testAutoFilterColumnObject->getJoin();
-        $this->assertEquals(AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_OR, $result);
+        self::assertEquals(AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_OR, $result);
     }
 
     public function testSetJoin()
     {
         $result = $this->testAutoFilterColumnObject->setJoin(AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_AND);
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
 
         $result = $this->testAutoFilterColumnObject->getJoin();
-        $this->assertEquals(AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_AND, $result);
+        self::assertEquals(AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_AND, $result);
     }
 
     /**
@@ -114,7 +114,7 @@ class ColumnTest extends PHPUnit_Framework_TestCase
 
         //    Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterColumnObject->setAttributes($attributeSet);
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
     }
 
     public function testGetAttributes()
@@ -127,8 +127,8 @@ class ColumnTest extends PHPUnit_Framework_TestCase
         $this->testAutoFilterColumnObject->setAttributes($attributeSet);
 
         $result = $this->testAutoFilterColumnObject->getAttributes();
-        $this->assertInternalType('array', $result);
-        $this->assertCount(count($attributeSet), $result);
+        self::assertInternalType('array', $result);
+        self::assertCount(count($attributeSet), $result);
     }
 
     public function testSetAttribute()
@@ -141,7 +141,7 @@ class ColumnTest extends PHPUnit_Framework_TestCase
         foreach ($attributeSet as $attributeName => $attributeValue) {
             //    Setters return the instance to implement the fluent interface
             $result = $this->testAutoFilterColumnObject->setAttribute($attributeName, $attributeValue);
-            $this->assertInstanceOf(AutoFilter\Column::class, $result);
+            self::assertInstanceOf(AutoFilter\Column::class, $result);
         }
     }
 
@@ -156,21 +156,21 @@ class ColumnTest extends PHPUnit_Framework_TestCase
 
         foreach ($attributeSet as $attributeName => $attributeValue) {
             $result = $this->testAutoFilterColumnObject->getAttribute($attributeName);
-            $this->assertEquals($attributeValue, $result);
+            self::assertEquals($attributeValue, $result);
         }
         $result = $this->testAutoFilterColumnObject->getAttribute('nonExistentAttribute');
-        $this->assertNull($result);
+        self::assertNull($result);
     }
 
     public function testClone()
     {
         $originalRule = $this->testAutoFilterColumnObject->createRule();
         $result = clone $this->testAutoFilterColumnObject;
-        $this->assertInstanceOf(AutoFilter\Column::class, $result);
-        $this->assertCount(1, $result->getRules());
-        $this->assertContainsOnlyInstancesOf(AutoFilter\Column\Rule::class, $result->getRules());
+        self::assertInstanceOf(AutoFilter\Column::class, $result);
+        self::assertCount(1, $result->getRules());
+        self::assertContainsOnlyInstancesOf(AutoFilter\Column\Rule::class, $result->getRules());
         $clonedRule = $result->getRules()[0];
-        $this->assertNotSame($originalRule, $clonedRule);
-        $this->assertSame($result, $clonedRule->getParent());
+        self::assertNotSame($originalRule, $clonedRule);
+        self::assertSame($result, $clonedRule->getParent());
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilterTest.php
index 974dbd70..3a922420 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilterTest.php
@@ -36,20 +36,20 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  magic __toString should return the active autofilter range
         $result = $this->testAutoFilterObject;
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testGetParent()
     {
         $result = $this->testAutoFilterObject->getParent();
-        $this->assertInstanceOf(Worksheet::class, $result);
+        self::assertInstanceOf(Worksheet::class, $result);
     }
 
     public function testSetParent()
     {
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setParent($this->mockWorksheetObject);
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
     }
 
     public function testGetRange()
@@ -58,7 +58,7 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Result should be the active autofilter range
         $result = $this->testAutoFilterObject->getRange();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     public function testSetRange()
@@ -71,11 +71,11 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         foreach ($ranges as $actualRange => $fullRange) {
             //  Setters return the instance to implement the fluent interface
             $result = $this->testAutoFilterObject->setRange($fullRange);
-            $this->assertInstanceOf(AutoFilter::class, $result);
+            self::assertInstanceOf(AutoFilter::class, $result);
 
             //  Result should be the new autofilter range
             $result = $this->testAutoFilterObject->getRange();
-            $this->assertEquals($actualRange, $result);
+            self::assertEquals($actualRange, $result);
         }
     }
 
@@ -85,11 +85,11 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setRange('');
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
 
         //  Result should be a clear range
         $result = $this->testAutoFilterObject->getRange();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
     }
 
     /**
@@ -106,8 +106,8 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
     {
         //  There should be no columns yet defined
         $result = $this->testAutoFilterObject->getColumns();
-        $this->assertInternalType('array', $result);
-        $this->assertCount(0, $result);
+        self::assertInternalType('array', $result);
+        self::assertCount(0, $result);
     }
 
     public function testGetColumnOffset()
@@ -122,7 +122,7 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         //    integer returned representing the column offset within the range
         foreach ($columnIndexes as $columnIndex => $columnOffset) {
             $result = $this->testAutoFilterObject->getColumnOffset($columnIndex);
-            $this->assertEquals($columnOffset, $result);
+            self::assertEquals($columnOffset, $result);
         }
     }
 
@@ -142,15 +142,15 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setColumn($expectedResult);
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
 
         $result = $this->testAutoFilterObject->getColumns();
         //  Result should be an array of \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column
         //    objects for each column we set indexed by the column ID
-        $this->assertInternalType('array', $result);
-        $this->assertCount(1, $result);
-        $this->assertArrayHasKey($expectedResult, $result);
-        $this->assertInstanceOf(Column::class, $result[$expectedResult]);
+        self::assertInternalType('array', $result);
+        self::assertCount(1, $result);
+        self::assertArrayHasKey($expectedResult, $result);
+        self::assertInstanceOf(Column::class, $result[$expectedResult]);
     }
 
     /**
@@ -170,15 +170,15 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setColumn($columnObject);
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
 
         $result = $this->testAutoFilterObject->getColumns();
         //  Result should be an array of \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column
         //    objects for each column we set indexed by the column ID
-        $this->assertInternalType('array', $result);
-        $this->assertCount(1, $result);
-        $this->assertArrayHasKey($expectedResult, $result);
-        $this->assertInstanceOf(Column::class, $result[$expectedResult]);
+        self::assertInternalType('array', $result);
+        self::assertCount(1, $result);
+        self::assertArrayHasKey($expectedResult, $result);
+        self::assertInstanceOf(Column::class, $result[$expectedResult]);
     }
 
     /**
@@ -214,11 +214,11 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         $result = $this->testAutoFilterObject->getColumns();
         //  Result should be an array of \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column
         //    objects for each column we set indexed by the column ID
-        $this->assertInternalType('array', $result);
-        $this->assertCount(count($columnIndexes), $result);
+        self::assertInternalType('array', $result);
+        self::assertCount(count($columnIndexes), $result);
         foreach ($columnIndexes as $columnIndex) {
-            $this->assertArrayHasKey($columnIndex, $result);
-            $this->assertInstanceOf(Column::class, $result[$columnIndex]);
+            self::assertArrayHasKey($columnIndex, $result);
+            self::assertInstanceOf(Column::class, $result[$columnIndex]);
         }
     }
 
@@ -234,7 +234,7 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         //    get a \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column object returned
         foreach ($columnIndexes as $columnIndex) {
             $result = $this->testAutoFilterObject->getColumn($columnIndex);
-            $this->assertInstanceOf(Column::class, $result);
+            self::assertInstanceOf(Column::class, $result);
         }
     }
 
@@ -250,8 +250,8 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         //    get a \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column object returned
         foreach ($columnIndexes as $columnIndex => $columnID) {
             $result = $this->testAutoFilterObject->getColumnByOffset($columnIndex);
-            $this->assertInstanceOf(Column::class, $result);
-            $this->assertEquals($result->getColumnIndex(), $columnID);
+            self::assertInstanceOf(Column::class, $result);
+            self::assertEquals($result->getColumnIndex(), $columnID);
         }
     }
 
@@ -260,7 +260,7 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         //  If we request a specific column by its column ID, we should
         //    get a \PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column object returned
         $result = $this->testAutoFilterObject->getColumn('K');
-        $this->assertInstanceOf(Column::class, $result);
+        self::assertInstanceOf(Column::class, $result);
     }
 
     /**
@@ -284,16 +284,16 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setRange('');
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
 
         //  Range should be cleared
         $result = $this->testAutoFilterObject->getRange();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
 
         //  Column array should be cleared
         $result = $this->testAutoFilterObject->getColumns();
-        $this->assertInternalType('array', $result);
-        $this->assertCount(0, $result);
+        self::assertInternalType('array', $result);
+        self::assertCount(0, $result);
     }
 
     public function testSetRangeWithExistingColumns()
@@ -313,17 +313,17 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
 
         //  Setters return the instance to implement the fluent interface
         $result = $this->testAutoFilterObject->setRange($expectedResult);
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
 
         //  Range should be correctly set
         $result = $this->testAutoFilterObject->getRange();
-        $this->assertEquals($expectedResult, $result);
+        self::assertEquals($expectedResult, $result);
 
         //  Only columns that existed in the original range and that
         //    still fall within the new range should be retained
         $result = $this->testAutoFilterObject->getColumns();
-        $this->assertInternalType('array', $result);
-        $this->assertCount(count($columnIndexes1), $result);
+        self::assertInternalType('array', $result);
+        self::assertCount(count($columnIndexes1), $result);
     }
 
     public function testClone()
@@ -335,6 +335,6 @@ class AutoFilterTest extends PHPUnit_Framework_TestCase
         }
 
         $result = clone $this->testAutoFilterObject;
-        $this->assertInstanceOf(AutoFilter::class, $result);
+        self::assertInstanceOf(AutoFilter::class, $result);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
index 5af397a5..20e71d81 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
@@ -34,11 +34,11 @@ class ColumnCellIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new ColumnCellIterator($this->mockWorksheet, 'A');
         $ColumnCellIndexResult = 1;
-        $this->assertEquals($ColumnCellIndexResult, $iterator->key());
+        self::assertEquals($ColumnCellIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $ColumnCell) {
-            $this->assertEquals($ColumnCellIndexResult++, $key);
-            $this->assertInstanceOf(Cell::class, $ColumnCell);
+            self::assertEquals($ColumnCellIndexResult++, $key);
+            self::assertInstanceOf(Cell::class, $ColumnCell);
         }
     }
 
@@ -46,11 +46,11 @@ class ColumnCellIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new ColumnCellIterator($this->mockWorksheet, 'A', 2, 4);
         $ColumnCellIndexResult = 2;
-        $this->assertEquals($ColumnCellIndexResult, $iterator->key());
+        self::assertEquals($ColumnCellIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $ColumnCell) {
-            $this->assertEquals($ColumnCellIndexResult++, $key);
-            $this->assertInstanceOf(Cell::class, $ColumnCell);
+            self::assertEquals($ColumnCellIndexResult++, $key);
+            self::assertInstanceOf(Cell::class, $ColumnCell);
         }
     }
 
@@ -59,11 +59,11 @@ class ColumnCellIteratorTest extends PHPUnit_Framework_TestCase
         $iterator = new ColumnCellIterator($this->mockWorksheet, 'A', 2, 4);
         $columnIndexResult = 4;
         $iterator->seek(4);
-        $this->assertEquals($columnIndexResult, $iterator->key());
+        self::assertEquals($columnIndexResult, $iterator->key());
 
         for ($i = 1; $i < $columnIndexResult - 1; ++$i) {
             $iterator->prev();
-            $this->assertEquals($columnIndexResult - $i, $iterator->key());
+            self::assertEquals($columnIndexResult - $i, $iterator->key());
         }
     }
 
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
index 3f107f45..0736fb16 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
@@ -31,11 +31,11 @@ class ColumnIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new ColumnIterator($this->mockWorksheet);
         $columnIndexResult = 'A';
-        $this->assertEquals($columnIndexResult, $iterator->key());
+        self::assertEquals($columnIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $column) {
-            $this->assertEquals($columnIndexResult++, $key);
-            $this->assertInstanceOf(Column::class, $column);
+            self::assertEquals($columnIndexResult++, $key);
+            self::assertInstanceOf(Column::class, $column);
         }
     }
 
@@ -43,11 +43,11 @@ class ColumnIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new ColumnIterator($this->mockWorksheet, 'B', 'D');
         $columnIndexResult = 'B';
-        $this->assertEquals($columnIndexResult, $iterator->key());
+        self::assertEquals($columnIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $column) {
-            $this->assertEquals($columnIndexResult++, $key);
-            $this->assertInstanceOf(Column::class, $column);
+            self::assertEquals($columnIndexResult++, $key);
+            self::assertInstanceOf(Column::class, $column);
         }
     }
 
@@ -57,12 +57,12 @@ class ColumnIteratorTest extends PHPUnit_Framework_TestCase
         $iterator = new ColumnIterator($this->mockWorksheet, 'B', 'D');
         $columnIndexResult = 'D';
         $iterator->seek('D');
-        $this->assertEquals($columnIndexResult, $iterator->key());
+        self::assertEquals($columnIndexResult, $iterator->key());
 
         for ($i = 1; $i < array_search($columnIndexResult, $ranges); ++$i) {
             $iterator->prev();
             $expectedResult = $ranges[array_search($columnIndexResult, $ranges) - $i];
-            $this->assertEquals($expectedResult, $iterator->key());
+            self::assertEquals($expectedResult, $iterator->key());
         }
     }
 
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
index edb76a55..7a040862 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
@@ -34,11 +34,11 @@ class RowCellIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new RowCellIterator($this->mockWorksheet);
         $RowCellIndexResult = 'A';
-        $this->assertEquals($RowCellIndexResult, $iterator->key());
+        self::assertEquals($RowCellIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $RowCell) {
-            $this->assertEquals($RowCellIndexResult++, $key);
-            $this->assertInstanceOf(Cell::class, $RowCell);
+            self::assertEquals($RowCellIndexResult++, $key);
+            self::assertInstanceOf(Cell::class, $RowCell);
         }
     }
 
@@ -46,11 +46,11 @@ class RowCellIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new RowCellIterator($this->mockWorksheet, 2, 'B', 'D');
         $RowCellIndexResult = 'B';
-        $this->assertEquals($RowCellIndexResult, $iterator->key());
+        self::assertEquals($RowCellIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $RowCell) {
-            $this->assertEquals($RowCellIndexResult++, $key);
-            $this->assertInstanceOf(Cell::class, $RowCell);
+            self::assertEquals($RowCellIndexResult++, $key);
+            self::assertInstanceOf(Cell::class, $RowCell);
         }
     }
 
@@ -60,12 +60,12 @@ class RowCellIteratorTest extends PHPUnit_Framework_TestCase
         $iterator = new RowCellIterator($this->mockWorksheet, 2, 'B', 'D');
         $RowCellIndexResult = 'D';
         $iterator->seek('D');
-        $this->assertEquals($RowCellIndexResult, $iterator->key());
+        self::assertEquals($RowCellIndexResult, $iterator->key());
 
         for ($i = 1; $i < array_search($RowCellIndexResult, $ranges); ++$i) {
             $iterator->prev();
             $expectedResult = $ranges[array_search($RowCellIndexResult, $ranges) - $i];
-            $this->assertEquals($expectedResult, $iterator->key());
+            self::assertEquals($expectedResult, $iterator->key());
         }
     }
 
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
index 071baf7d..629f66e0 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
@@ -31,11 +31,11 @@ class RowIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new RowIterator($this->mockWorksheet);
         $rowIndexResult = 1;
-        $this->assertEquals($rowIndexResult, $iterator->key());
+        self::assertEquals($rowIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $row) {
-            $this->assertEquals($rowIndexResult++, $key);
-            $this->assertInstanceOf(Row::class, $row);
+            self::assertEquals($rowIndexResult++, $key);
+            self::assertInstanceOf(Row::class, $row);
         }
     }
 
@@ -43,11 +43,11 @@ class RowIteratorTest extends PHPUnit_Framework_TestCase
     {
         $iterator = new RowIterator($this->mockWorksheet, 2, 4);
         $rowIndexResult = 2;
-        $this->assertEquals($rowIndexResult, $iterator->key());
+        self::assertEquals($rowIndexResult, $iterator->key());
 
         foreach ($iterator as $key => $row) {
-            $this->assertEquals($rowIndexResult++, $key);
-            $this->assertInstanceOf(Row::class, $row);
+            self::assertEquals($rowIndexResult++, $key);
+            self::assertInstanceOf(Row::class, $row);
         }
     }
 
@@ -56,11 +56,11 @@ class RowIteratorTest extends PHPUnit_Framework_TestCase
         $iterator = new RowIterator($this->mockWorksheet, 2, 4);
         $columnIndexResult = 4;
         $iterator->seek(4);
-        $this->assertEquals($columnIndexResult, $iterator->key());
+        self::assertEquals($columnIndexResult, $iterator->key());
 
         for ($i = 1; $i < $columnIndexResult - 1; ++$i) {
             $iterator->prev();
-            $this->assertEquals($columnIndexResult - $i, $iterator->key());
+            self::assertEquals($columnIndexResult - $i, $iterator->key());
         }
     }
 
diff --git a/tests/PhpSpreadsheetTests/Worksheet/WorksheetColumnTest.php b/tests/PhpSpreadsheetTests/Worksheet/WorksheetColumnTest.php
index c8730e25..56514fa5 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/WorksheetColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/WorksheetColumnTest.php
@@ -25,23 +25,23 @@ class WorksheetColumnTest extends PHPUnit_Framework_TestCase
     public function testInstantiateColumnDefault()
     {
         $column = new Column($this->mockWorksheet);
-        $this->assertInstanceOf(Column::class, $column);
+        self::assertInstanceOf(Column::class, $column);
         $columnIndex = $column->getColumnIndex();
-        $this->assertEquals('A', $columnIndex);
+        self::assertEquals('A', $columnIndex);
     }
 
     public function testInstantiateColumnSpecified()
     {
         $column = new Column($this->mockWorksheet, 'E');
-        $this->assertInstanceOf(Column::class, $column);
+        self::assertInstanceOf(Column::class, $column);
         $columnIndex = $column->getColumnIndex();
-        $this->assertEquals('E', $columnIndex);
+        self::assertEquals('E', $columnIndex);
     }
 
     public function testGetCellIterator()
     {
         $column = new Column($this->mockWorksheet);
         $cellIterator = $column->getCellIterator();
-        $this->assertInstanceOf(ColumnCellIterator::class, $cellIterator);
+        self::assertInstanceOf(ColumnCellIterator::class, $cellIterator);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Worksheet/WorksheetRowTest.php b/tests/PhpSpreadsheetTests/Worksheet/WorksheetRowTest.php
index d16149fb..e81f821e 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/WorksheetRowTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/WorksheetRowTest.php
@@ -25,23 +25,23 @@ class WorksheetRowTest extends PHPUnit_Framework_TestCase
     public function testInstantiateRowDefault()
     {
         $row = new Row($this->mockWorksheet);
-        $this->assertInstanceOf(Row::class, $row);
+        self::assertInstanceOf(Row::class, $row);
         $rowIndex = $row->getRowIndex();
-        $this->assertEquals(1, $rowIndex);
+        self::assertEquals(1, $rowIndex);
     }
 
     public function testInstantiateRowSpecified()
     {
         $row = new Row($this->mockWorksheet, 5);
-        $this->assertInstanceOf(Row::class, $row);
+        self::assertInstanceOf(Row::class, $row);
         $rowIndex = $row->getRowIndex();
-        $this->assertEquals(5, $rowIndex);
+        self::assertEquals(5, $rowIndex);
     }
 
     public function testGetCellIterator()
     {
         $row = new Row($this->mockWorksheet);
         $cellIterator = $row->getCellIterator();
-        $this->assertInstanceOf(RowCellIterator::class, $cellIterator);
+        self::assertInstanceOf(RowCellIterator::class, $cellIterator);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/WorksheetTest.php b/tests/PhpSpreadsheetTests/WorksheetTest.php
index 1a7389b0..5605fc81 100644
--- a/tests/PhpSpreadsheetTests/WorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/WorksheetTest.php
@@ -14,7 +14,7 @@ class WorksheetTest extends PHPUnit_Framework_TestCase
 
         $worksheet = new Worksheet();
         $worksheet->setTitle($testTitle);
-        $this->assertSame($testTitle, $worksheet->getTitle());
+        self::assertSame($testTitle, $worksheet->getTitle());
     }
 
     public function setTitleInvalidProvider()
@@ -53,17 +53,17 @@ class WorksheetTest extends PHPUnit_Framework_TestCase
         // Set unique title -- should be unchanged
         $sheet = $spreadsheet->getSheet(0);
         $sheet->setTitle('Test Title');
-        $this->assertSame('Test Title', $sheet->getTitle());
+        self::assertSame('Test Title', $sheet->getTitle());
 
         // Set duplicate title -- should have numeric suffix appended
         $sheet = $spreadsheet->getSheet(1);
         $sheet->setTitle('Test Title');
-        $this->assertSame('Test Title 1', $sheet->getTitle());
+        self::assertSame('Test Title 1', $sheet->getTitle());
 
         // Set duplicate title with validation disabled -- should be unchanged
         $sheet = $spreadsheet->getSheet(2);
         $sheet->setTitle('Test Title', true, false);
-        $this->assertSame('Test Title', $sheet->getTitle());
+        self::assertSame('Test Title', $sheet->getTitle());
     }
 
     public function testSetCodeName()
@@ -72,7 +72,7 @@ class WorksheetTest extends PHPUnit_Framework_TestCase
 
         $worksheet = new Worksheet();
         $worksheet->setCodeName($testCodeName);
-        $this->assertSame($testCodeName, $worksheet->getCodeName());
+        self::assertSame($testCodeName, $worksheet->getCodeName());
     }
 
     public function setCodeNameInvalidProvider()
@@ -111,16 +111,16 @@ class WorksheetTest extends PHPUnit_Framework_TestCase
         // Set unique code name -- should be massaged to Snake_Case
         $sheet = $spreadsheet->getSheet(0);
         $sheet->setCodeName('Test Code Name');
-        $this->assertSame('Test_Code_Name', $sheet->getCodeName());
+        self::assertSame('Test_Code_Name', $sheet->getCodeName());
 
         // Set duplicate code name -- should be massaged and have numeric suffix appended
         $sheet = $spreadsheet->getSheet(1);
         $sheet->setCodeName('Test Code Name');
-        $this->assertSame('Test_Code_Name_1', $sheet->getCodeName());
+        self::assertSame('Test_Code_Name_1', $sheet->getCodeName());
 
         // Set duplicate code name with validation disabled -- should be unchanged, and unmassaged
         $sheet = $spreadsheet->getSheet(2);
         $sheet->setCodeName('Test Code Name', false);
-        $this->assertSame('Test Code Name', $sheet->getCodeName());
+        self::assertSame('Test Code Name', $sheet->getCodeName());
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php b/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
index 00cf5cc5..87bd7310 100644
--- a/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
@@ -42,7 +42,7 @@ class ContentTest extends PHPUnit_Framework_TestCase
         $content = new Content(new Ods(new Spreadsheet()));
         $xml = $content->write();
 
-        $this->assertXmlStringEqualsXmlFile($this->samplesPath . '/content-empty.xml', $xml);
+        self::assertXmlStringEqualsXmlFile($this->samplesPath . '/content-empty.xml', $xml);
     }
 
     public function testWriteSpreadsheet()
@@ -93,6 +93,6 @@ class ContentTest extends PHPUnit_Framework_TestCase
         $content = new Content(new Ods($workbook));
         $xml = $content->write();
 
-        $this->assertXmlStringEqualsXmlFile($this->samplesPath . '/content-with-data.xml', $xml);
+        self::assertXmlStringEqualsXmlFile($this->samplesPath . '/content-with-data.xml', $xml);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
index 72c2f470..0fd9dbad 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
@@ -46,7 +46,7 @@ class WorkbookTest extends PHPUnit_Framework_TestCase
 
         $palette = $propertyPalette->getValue($this->workbook);
 
-        $this->assertEquals($expectedResult, $palette);
+        self::assertEquals($expectedResult, $palette);
     }
 
     public function providerAddColor()