如何对@viewChild ElementRef angular 进行单元测试

Question

My component file has the following code

@ViewChild('clusterCard', { static: false }) clusterCard: ElementRef;



highLightTheClusterCard(point: PickupClusterPoint) {
    if (point) {
      const card: HTMLElement = _get(this.clusterCard, 'nativeElement');
      const selectedPoint: PositioningPoint = this.lane.data.selectedPostioningPoint;

      /* if card is available, position point of the card and the cluster is same and infowindow over the cluster is open then
         highlight the card */
      if (card && _isEqual(point.pointData, selectedPoint) && point.openInfoWindow) {
        card.scrollIntoView();
        card['style'].borderLeft = `5px solid ${this.lane.data.color || 'transparent'}`;
      } else {
        card['style'].borderLeft = `5px solid transparent`;
      }
    }
  }

  ngAfterViewChecked(): void {
    ...some code

    this.pickupClusterPointsService.positioningPoint$
      .pipe(skip(1), takeUntil(this.unsubscriber.done))
      .subscribe((point: PickupClusterPoint) => {
        this.highLightTheClusterCard(point);
      });
  }

HTML file

    <div #clusterCard>
      <pickup-cluster-stop-card
       ..some code
      >
      </pickup-cluster-stop-card>
    </div>

I want to unit test the highLightTheClusterCard method. I am getting

TypeError: Cannot read property 'pipe' of undefined error properties

and TypeError: Cannot set property 'borderLeft' of undefined at

Unit test file

  beforeEach(() => {
   
     ...some code

    fixture = TestBed.createComponent(RouteLaneComponent);
    component = fixture.componentInstance;

    ....some code

    fixture.detectChanges();
  });

  fdescribe('highLightTheClusterCard', () => {
     it('should expect cluster card to be defined ', () => {
        // component.clusterCard.nativeElement = new HTMLElement();
        component.clusterCard = new ElementRef({ nativeElement: jasmine.createSpyObj('nativeElement', ['scrollIntoView', 'style'])});
        component.highLightTheClusterCard({ pointData: new PositioningPoint(), openInfoWindow: true} as PickupClusterPoint);
        // expect(component.clusterCard).toBeDefined();
         // expect(component.clusterCard.nativeElement.scrollIntoView).toHaveBeenCalled();
     });
  });

I read this How to mock a nativeElement.focus() in Angular 4 spec file

but still, I am unable to make it green.

  MockService(PickupClusterPointsService, {
          ...more code
          positioningPoint$: of(undefined),
        }),  

Solution: I have added positioningPoint$: of(undefined) in mock service. MockService is inside the Provider. you can see above lines.

describe('highLightTheClusterCard', () => {
        it('should expect cluster card to be highlighted when hover over infowindow ', () => {
            component.lane.data.selectedPostioningPoint = new PositioningPoint();
            component.lane.data.color = '#2196F3';
            component.clusterCard = {
              nativeElement: jasmine.createSpyObj('nativeElement', ['scrollIntoView', 'style'])
            };
    
           component.highLightTheClusterCard({ pointData: new PositioningPoint(), openInfoWindow: true} as PickupClusterPoint);
    
           expect(component.clusterCard).toBeDefined();
           expect(component.clusterCard.nativeElement.scrollIntoView).toHaveBeenCalled();
           expect(component.clusterCard.nativeElement.style.borderLeft).toBe('5px solid #2196F3');
        });
        it('should expect cluster card not to be highlighted when hover out from the infowindow', () => {
          component.lane.data.selectedPostioningPoint = new PositioningPoint();
          component.clusterCard = {
            nativeElement: jasmine.createSpyObj('nativeElement', ['scrollIntoView', 'style'])
          };
         component.highLightTheClusterCard({ pointData: new PositioningPoint(), openInfoWindow: false} as PickupClusterPoint);
    
         expect(component.clusterCard).toBeDefined();
         expect(component.clusterCard.nativeElement.style.borderLeft).toBe('5px solid transparent');
      });
     });

Answer 1

You have several issues it seems.

Your first error

TypeError: Cannot read property 'pipe' of undefined error properties

come from that you haven't instantiated your pickupClusterPointsService service properly.

The second error

TypeError: Cannot set property 'borderLeft' of undefined at

I'm not sure just yet

Answer 2

You have created your spy with "style" as a function of native element

jasmine.createSpyObj('nativeElement', ['scrollIntoView', 'style'])

instead of property

jasmine.createSpyObj('nativeElement', ['scrollIntoView'], {style: {}])

Therefore TypeError: Cannot set property 'borderLeft' of undefined is because in card['style'].borderLeft , card['style'] doesn't exist.