xny/vendor/phpoffice/phpspreadsheet/samples/Calculations/DateTime/EOMONTH.php

<?php

use PhpOffice\PhpSpreadsheet\Spreadsheet;

require __DIR__ . '/../../Header.php';

$category = 'Date/Time';
$functionName = 'EOMONTH';
$description = 'Returns the serial number for the last day of the month that is the indicated number of months before or after start_date';

$helper->titles($category, $functionName, $description);

// Create new PhpSpreadsheet object
$spreadsheet = new Spreadsheet();
$worksheet = $spreadsheet->getActiveSheet();

$months = range(-12, 12);
$testDateCount = count($months);

for ($row = 1; $row <= $testDateCount; ++$row) {
    $worksheet->setCellValue('A' . $row, '=DATE(2020,1,1)');
    $worksheet->setCellValue('B' . $row, '=A' . $row);
    $worksheet->setCellValue('C' . $row, $months[$row - 1]);
    $worksheet->setCellValue('D' . $row, '=EOMONTH(B' . $row . ', C' . $row . ')');
}
$worksheet->getStyle('B1:B' . $testDateCount)
    ->getNumberFormat()
    ->setFormatCode('yyyy-mm-dd');

$worksheet->getStyle('D1:D' . $testDateCount)
    ->getNumberFormat()
    ->setFormatCode('yyyy-mm-dd');

// Test the formulae
for ($row = 1; $row <= $testDateCount; ++$row) {
    $helper->log(sprintf(
        '%s and %d months is %d (%s)',
        $worksheet->getCell('B' . $row)->getFormattedValue(),
        $worksheet->getCell('C' . $row)->getFormattedValue(),
        $worksheet->getCell('D' . $row)->getCalculatedValue(),
        $worksheet->getCell('D' . $row)->getFormattedValue()
    ));
}