setActiveSheetIndex(0); $spreadsheet->getActiveSheet()->setCellValue('A1', '1'); $spreadsheet->getActiveSheet()->setCellValue('B1', '2'); $spreadsheet->getActiveSheet()->setCellValue('A2', '33'); $spreadsheet->getActiveSheet()->mergeCells('A2:B2'); $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, $format); $actual = 0; foreach ($reloadedSpreadsheet->getWorksheetIterator() as $worksheet) { $actual += count($worksheet->getMergeCells()); } self::assertSame(1, $actual, "Format $format failed, could not read 1 merged cell"); } }