CODEWITHSUNDEEP
angularunit-testingtypescriptkarma-jasmineangular-directive
Chrillewoodz
Chrillewoodz

Reputation: 28368

Angular - unit test spy are not recognising that the function has been called

I've got a test component that I use for testing directives:

export class UnitTestComponent implements OnInit {
  @ViewChild(BackgroundLoadedDirective) backgroundLoaded: BackgroundLoadedDirective;

  public url = 'https://www.codeproject.com/KB/GDI-plus/ImageProcessing2/flip.jpg';

  constructor() {}

  ngOnInit() {}

  loaded(): void {
    console.log(true)
  }
}

Then I have this directive which I would like to write some tests for:

@Directive({
  selector: '[backgroundLoaded]'
})

export class BackgroundLoadedDirective {
  @Input('backgroundLoaded') set url(value) {
    this.createImage(value);
  };

  get url() {
    return this._url;
  }

  @Output() loaded: EventEmitter<any> = new EventEmitter<any>();

  public img: HTMLImageElement;

  private _url: string;

  @HostBinding('class.background-loaded')
  isLoaded = false;

  createImage(url: string): void {

    // This gets logged as expected
    console.log(url);

    this._url = url;

    this.img = new Image();

    this.img.onload = () => {
      this.isLoaded = true;
      this.load.emit(url);
    };

    this.img.src = url;
  }
}

Then I have just this test so far:

describe('BackgroundLoadedDirective', () => {

  let component: UnitTestComponent;
  let fixture: ComponentFixture<UnitTestComponent>;
  let spy: any;

  beforeEach(() => {

    TestBed.configureTestingModule({
      declarations: [
        UnitTestComponent,
        BackgroundLoadedDirective
      ],
      schemas: [NO_ERRORS_SCHEMA],
      providers: [
        {provide: ComponentFixtureAutoDetect, useValue: true}
      ]
    });

    fixture = TestBed.createComponent(UnitTestComponent);
    component = fixture.componentInstance;
  });

  it('should create a fake img tag', () => {

    spy = spyOn(component.backgroundLoaded, 'createImage').and.callThrough();

    expect(component.backgroundLoaded.img).toBeTruthy();
    expect(spy).toHaveBeenCalled();
  });
});

The problem is that the test fails saying:

Expected spy createImage to have been called.

Why isn't the spy working despite the function being called?

EDIT:

Just to clarify, this is the test component's html which applies the directive and gives it the url.

<div [urlToBackground]="url" [backgroundLoaded]="url" (loaded)="loaded($event)"></div>

Upvotes: 2

Views: 2716

Answers (1)

malifa
malifa

Reputation: 8165

Basically what's interfering are angulars lifecycle hooks. Your test just doesn't cares enough in terms of timing.

To make it easier to test, trigger a change and then test if your setter works (and calls the function you're spying on).

Something like this:

it('should create a fake img tag', () => {
    let spy: jasmine.Spy = spyOn(component.backgroundLoaded, 'createImage').and.callThrough();

    comp.backgroundLoaded.url = 'foobar';
    fixture.detectChanges(); // wait for the change detection to kick in

    expect(spy).toHaveBeenCalled();
});

Hope it helps.

(edit: removed one detectChanges() for ngOnInit, because it's not needed here and should be called before the test anyway)

Upvotes: 3

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