describe('app-component', () => {
  // We are going to test AppComponent.
  // Therefore, we want to mock its dependencies,
  // they are declared and imported in the module
  // where AppComponent has been declared too.
  // The next line says mock everything in AppModule,
  // but keep AppComponent as it is.
  beforeEach(() => {
    // The result of MockBuilder should be returned.
    return MockBuilder(AppComponent, AppModule);
  });

  // Stubbing observables in AuthService for all tests in the suite.
  beforeEach(() =>
    MockInstance(AuthService, () => ({
      isLoggedIn$: EMPTY,
      currentUser$: EMPTY,
    })),
  );

  it('should be created and initialized', () => {
    // Creating a spy on the 'check' method of the service.
    // MockInstance allows to spy / stub properties and methods
    // of declarations and providers before their instances
    // have been initialized.
    const spyCheck = MockInstance(
      AuthService,
      'check',
      jasmine.createSpyObj('AuthService.check'),
    ).and.returnValue(true);

    const fixture = MockRender(AppComponent);
    // Checking that the component has been created.
    expect(fixture.point.componentInstance).toBeDefined();
    // Checking that its ngOnInit method calls 'check' of the service.
    expect(spyCheck).toHaveBeenCalled();
  });
});