PhpSpreadsheet/tests/data/Calculation/Functions/ISFORMULA.php

<?php

return [
    [
        false,
        null,
    ],
    [
        false,
        -1,
    ],
    [
        false,
        0,
    ],
    [
        false,
        1,
    ],
    [
        false,
        '',
    ],
    [
        false,
        '2',
    ],
    [
        false,
        '#VALUE!',
    ],
    [
        false,
        '#N/A',
    ],
    [
        false,
        'TRUE',
    ],
    [
        false,
        true,
    ],
    [
        false,
        false,
    ],
    [
        true,
        '="ABC"',
    ],
    [
        true,
        '=A1',
    ],
    [
        '#REF!',
    ],
];