How to center text \"test\"?
This is my code:
        
if you want to align only this cells, you can do something like this:
    $style = array(
        'alignment' => array(
            'horizontal' => PHPExcel_Style_Alignment::HORIZONTAL_CENTER,
        )
    );
    $sheet->getStyle("A1:B1")->applyFromArray($style);
But, if you want to apply this style to all cells, try this:
    $style = array(
        'alignment' => array(
            'horizontal' => PHPExcel_Style_Alignment::HORIZONTAL_CENTER,
        )
    );
    $sheet->getDefaultStyle()->applyFromArray($style);