Tester\Environment::lock PHP Method

    public static function lock($name = '', $path = '')
    {
        static $locks;
        $file = "{$path}/lock-" . md5($name);
        if (!isset($locks[$file])) {
            flock($locks[$file] = fopen($file, 'w'), LOCK_EX);
        }
    }

 public function setUp()
 {
     if (static::$serial) {
         // serialize report test because of database connection
         Environment::lock('db', dirname(TEMP_DIR));
     }
 }