public function testCallingAContainerCallable()
 {
     $settings = ['foo' => function ($c) {
         return function ($a) {
             return $a;
         };
     }];
     $app = new App($settings);
     $result = $app->foo('bar');
     $this->assertSame('bar', $result);
     $headers = new Headers();
     $body = new Body(fopen('php://temp', 'r+'));
     $request = new Request('GET', Uri::createFromString(''), $headers, [], [], $body);
     $response = new Response();
     $response = $app->notFoundHandler($request, $response);
     $this->assertSame(404, $response->getStatusCode());
 }