Initial unit test for locale floats (#1304)

* Initial unit test for locale floats
This will require potential modification of the TravisCI environment to support other locales

* var_dump to check output on TravisCI

* Fix assertions for double/float and with/without line reference

* Style in unit test

tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php

@@ -0,0 +1,58 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
+
+use PHPUnit\Framework\TestCase;
+
+class LocaleFloatsTest extends TestCase
+{
+    protected $localeAdjusted;
+
+    protected $currentLocale;
+
+    public function setUp()
+    {
+        $this->currentLocale = setlocale(LC_ALL, '0');
+
+        if (!setlocale(LC_ALL, 'fr_FR.UTF-8')) {
+            $this->localeAdjusted = false;
+
+            return;
+        }
+
+        $this->localeAdjusted = true;
+    }
+
+    public function tearDown()
+    {
+        if ($this->localeAdjusted) {
+            setlocale(LC_ALL, $this->currentLocale);
+        }
+    }
+
+    public function testLocaleFloatsCorrectlyConvertedByWriter()
+    {
+        if (!$this->localeAdjusted) {
+            $this->markTestSkipped('Unable to set locale for testing.');
+        }
+
+        $spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
+        $spreadsheet->getActiveSheet()->setCellValue('A1', 1.1);
+
+        $filename = 'decimalcomma.xlsx';
+        $writer = new \PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
+        $writer->save($filename);
+
+        $reader = new \PhpOffice\PhpSpreadsheet\Reader\Xlsx();
+        $spreadsheet = $reader->load($filename);
+
+        $result = $spreadsheet->getActiveSheet()->getCell('A1')->getValue();
+
+        ob_start();
+        var_dump($result);
+        preg_match('/(?:double|float)\(([^\)]+)\)/mui', ob_get_clean(), $matches);
+        $this->assertArrayHasKey(1, $matches);
+        $actual = $matches[1];
+        $this->assertEquals('1,1', $actual);
+    }
+}