Dingo\Api\Http\Response::setFormatters PHP Method

    public static function setFormatters(array $formatters)
    {
        static::$formatters = $formatters;
    }

 public function setUp()
 {
     $this->events = new Dispatcher();
     $this->config = new Properties('v1', null, null, 'testing', 'json', false);
     $this->router = new Router($this->events, $this->config);
     Response::setFormatters(['json' => new JsonResponseFormat()]);
 }