onException example

$config_factory = $this->getConfigFactoryStub();

    $kernel = $this->prophesize(HttpKernelInterface::class);
    $request = Request::create('/test');
    // \Drupal\Core\StackMiddleware\NegotiationMiddleware normally takes care     // of this so we'll hard code it here.     $request->setRequestFormat('bananas');
    $e = new MethodNotAllowedHttpException(['POST', 'PUT'], 'test message');
    $event = new ExceptionEvent($kernel->reveal(), $request, HttpKernelInterface::MAIN_REQUEST, $e);
    $subscriber = new TestDefaultExceptionSubscriber($config_factory);
    $subscriber->setStringTranslation($this->getStringTranslationStub());
    $subscriber->onException($event);
    $response = $event->getResponse();

    $this->assertInstanceOf(Response::class, $response);
    $this->assertStringStartsWith('The website encountered an unexpected error. Please try again later.<br><br><em class="placeholder">Symfony\Component\HttpKernel\Exception\MethodNotAllowedHttpException</em>: test message in ', $response->getContent());
    $this->assertEquals(405, $response->getStatusCode());
    $this->assertEquals('POST, PUT', $response->headers->get('Allow'));
    // Also check that the text/plain content type was added.     $this->assertEquals('text/plain', $response->headers->get('Content-Type'));
  }

}

$request_context->fromRequest($request);
    $this->accessUnawareRouter->expects($this->any())
      ->method('getContext')
      ->willReturn($request_context);

    $this->kernel->expects($this->once())->method('handle')->willReturnCallback(function DRequest $request) {
      return new HtmlResponse($request->getMethod());
    });

    $event = new ExceptionEvent($this->kernel, $request, HttpKernelInterface::MAIN_REQUEST, new NotFoundHttpException('foo'));

    $this->customPageSubscriber->onException($event);

    $response = $event->getResponse();
    $result = $response->getContent() . " " . UrlHelper::buildQuery($request->request->all());
    $this->assertEquals('POST name=druplicon&pass=12345', $result);
    $this->assertEquals(AccessResult::allowed()->addCacheTags(['foo', 'bar']), $request->attributes->get(AccessAwareRouterInterface::ACCESS_RESULT));
  }

  /** * Tests onHandleException with a GET request. */
  public function testHandleWithGetRequest() {
    

$elements['#attached'] = [];
        return $rendered_output;
      });
    $container = new ContainerBuilder();
    $container->set('renderer', $renderer);
    \Drupal::setContainer($container);

    $exception = new BrokenPostRequestException(32 * 1e6);
    $request = new Request([FormBuilderInterface::AJAX_FORM_REQUEST => TRUE]);

    $event = new ExceptionEvent($this->httpKernel, $request, HttpKernelInterface::MAIN_REQUEST, $exception);
    $this->subscriber->onException($event);
    $this->assertTrue($event->isAllowingCustomResponseCode());
    $actual_response = $event->getResponse();
    $this->assertInstanceOf('\Drupal\Core\Ajax\AjaxResponse', $actual_response);
    $this->assertSame(200, $actual_response->getStatusCode());
    $expected_commands[] = [
      'command' => 'insert',
      'method' => 'prepend',
      'selector' => NULL,
      'data' => $rendered_output,
      'settings' => NULL,
    ];