Angular2, Karma: failure requests that are not failing

While working on writing test cases for a modified version of the Angular.io Heroes tutorial, I encountered an interesting issue with one of the components. No matter what I tried, I couldn't get this particular test to fail.

Here's an example of the code:

describe('OrgDetailComponent', () => {

  let comp: OrgDetailComponent;
  let fixture: ComponentFixture<OrgDetailComponent>;
  let de: DebugElement;
  let el: HTMLElement;

  let org1: Org = new Org({ ... fills Org ... });

  let dialogService: DialogService = null;
  let globalsService: GlobalsService = null;
  let orgService: OrgService = null;
  let routeStub: any = { data: Observable.of( { org: org1 } ) } ;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [ FormsModule, RouterTestingModule ],
      providers : [
          { provide: DialogService, useClass: MockDialogService },
          { provide: GlobalsService, useClass: MockGlobalsService },
          { provide: OrgService, useClass: MockOrgService },
          { provide: ActivatedRoute, useValue: routeStub }          
      ],
      declarations: [ OrgDetailComponent ],
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(OrgDetailComponent);

    dialogService = fixture.debugElement.injector.get(DialogService);
    globalsService = fixture.debugElement.injector.get(GlobalsService);
    orgService = fixture.debugElement.injector.get(OrgService);
  });

  it('should always fail', () => { 
    fixture.detectChanges();
    fixture.whenStable().then(() => {
      fail('forced fail');
    });    
  });

});

Running this test did not yield any failures. Even after wrapping the fail statement in a try-catch block, the test still passed without triggering the catch block. The Karma testing framework consistently reported success. Why is that?

This issue is quite important as it prevents me from ensuring the accuracy of my tests. Despite knowing there were errors in the code, fixing just one issue made all error messages disappear. Without being able to clearly identify failures, the validity of the entire test suite comes into question.

I would appreciate any insights or solutions. Thank you, Jerome.

Answer №1

When using <code>fixture.whenStable()
, it is important to remember that it resolves asynchronously. To ensure the test waits for this resolution, you must use async

import { async } from '@angular/core/testing'

it('should always fail', async(() => { 
  fixture.detectChanges();
  fixture.whenStable().then(() => {
    fail('forced fail');
  });    
}));

By wrapping the test in async, Angular will wait for all asynchronous tasks to complete before finishing the test. If you omit async, the test may finish before whenStable() resolves.

This concept is similar to using beforeEach(async((). The compileComponents call also resolves asynchronously, so we use async to wait for it to finish.

Alternatively, you can utilize the fakeAsync/tick method combination to mimic synchronous behavior in tests by forcibly resolving async tasks with tick

import { fakeAsync, tick } from '@angular/core/testing'

it('should always fail', fakeAsync(() => { 
  fixture.detectChanges();
  tick()
  expect(...)    
}));

If fixture.detectChanges() triggers asynchronous tasks, calling tick() will ensure these tasks are completed before treating the test as synchronous.

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