Test mit Selektoren und Spy's

test.spec.ts

it('should edit an element via button click', async(() => {
       fixture.detectChanges();
       const compiled = fixture.debugElement.nativeElement;
       let matCards = compiled.querySelectorAll('mat-card');
       expect(app.toDoList.length).toBe(matCards.length);
       spyOn(app, 'openDialogEdit').and.callFake(() => {
         app.editItem(1, {name: 'Edit'});
       });
       const deleteElement = compiled.querySelectorAll('button.edit');
       deleteElement[0].click();
       fixture.detectChanges();
       fixture.whenStable().then(() => {
         matCards = compiled.querySelectorAll('mat-card');
         expect(4).toBe(matCards.length);
       });
     }));