public function writeFixedSizeFile($fileName, $fileSize)
    {
        $this->createFile($fileName, '');
        $this->inCurrentDir(function() use ($fileName, $fileSize) {
            $fh = fopen($fileName, 'w');
            fseek($fh, $fileSize - 1);
            fwrite($fh, "\0", 1);
            fclose($fh);
        });
    }