assertResponseFromException example

$exception = new FormAjaxException($form, $form_state);

    $request = new Request([], ['form_build_id' => 'the_build_id']);
    $commands = [];
    $response = new Response('');

    $this->formAjaxResponseBuilder->expects($this->once())
      ->method('buildResponse')
      ->with($request, $expected_form, $form_state, $commands)
      ->willReturn($response);

    $this->assertResponseFromException($request, $exception, $response);
    $this->assertTrue($this->event->isAllowingCustomResponseCode());
    $this->assertSame(200, $this->event->getResponse()->getStatusCode());
  }

  /** * @covers ::onException */
  public function testOnExceptionNewBuildId() {
    $form = ['#type' => 'form', '#build_id' => 'the_build_id'];
    $expected_form = $form + [
      '#build_id_old' => 'a_new_build_id',
    ];