PhpSpreadsheet/tests/data/Calculation/TextData/LEN.php

<?php

return [
    [
        null,
        0,
    ],
    [
        '',
        0,
    ],
    [
        'AbCdEfGhI',
        9,
    ],
    [
        'MARK BAKER',
        10,
    ],
    [
        true,
        4,
    ],
    [
        false,
        5,
    ],
];