Creating Excel file using PhpSpreadsheet with default headers from Array using Laravel 5.5

I am trying to download excel file with pre-populated headers using PhpSpreadsheet in laravel. But I am got empty file downloaded.Here`s my code.

use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Xlsx;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();
$sheet->setCellValue('B1','testing');

$writer = new Xlsx($spreadsheet);
$filename = 'tessa';

header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
header('Content-Disposition: attachment;filename="'. $filename .'.Xlsx"');
header('Cache-Control: max-age=0');

$writer->save($filename);

I tried dd($sheet) Here how it looks,it contains my data;

The file downloaded but empty file.Can any one tell me how to solve the issue?

via Chebli Mohamed