How to test form.valueChanges in Angular?

Question

How to correctly unit test (Karma, Jasmine), that emmisions of valueChanges dispatches a FormUpdated action?

beforeEach(async(() => {
  TestBed.configureTestingModule({
    imports: [...],
    providers: [
      { provide: Store, useValue: MOCK_STORE },
    ],
    declarations: [FormComponent],
    schemas: [NO_ERRORS_SCHEMA]
  })
    .compileComponents();
}));

beforeEach(() => {
    fixture = TestBed.createComponent(FormComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
});

export class FormComponent implements OnInit {
    searchForm: FormGroup;

    constructor(private readonly fb: FormBuilder, private readonly store: Store<AppState>) {
    }

    ngOnInit(): void {
        this.searchForm = this.fb.group({});
        this.searchForm.valueChanges.subscribe(value => this.store.dispatch(new FormUpdated(value)));
    }
}

I have tried something like this:

it('should dispatch action for valueChanges', () => {
    const spy = spyOn(component['store'], 'dispatch');
    spyOn(component.searchForm, 'valueChanges').and.returnValue(of({}));

    expect(spy).toHaveBeenCalledTimes(1);
});

But this does not work - the spy has not been called.

[Edit1] - Based on comments and answer:

The problem is with the test asynchronicity. Some part of ngOnInit calls setTimeout(() => this.searchForm.get('field').updateValueAndValidity();)) which causes an emmision to this.searchForm.valueChanges() so the this.store.dispatch is actually called but after the expect(spy).toHaveBeenCalledTimes(1).

I have tried to add fakeAsync(), tick() and flushMicrotasks() but with same outcome.

it('should dispatch action for valueChanges', () => {
    const spy = spyOn(component['store'], 'dispatch');
    spyOn(component.searchForm, 'valueChanges').and.returnValue(of({}));

    tick();
    flushMicrotasks();

    expect(spy).toHaveBeenCalledTimes(1);
});

Solution

You want to test changes on a form without inputs. Maybe try with this :

this.searchForm = this.fb.group({description: ['your_input']});

.

beforeEach(async(() => {
  TestBed.configureTestingModule({
    imports: [...],
    providers: [
      { provide: Store, useValue: MOCK_STORE },
    ],
    declarations: [FormComponent],
    schemas: [NO_ERRORS_SCHEMA]
  })
    .compileComponents();
}));

beforeEach(() => {
    fixture = TestBed.createComponent(FormComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
});

it('should dispatch action for valueChanges', () => {
    const spy = spyOn(TestBed.get(Store<AppState>), 'dispatch') 
    component.searchForm.controls['your_input'].setValue('test') // This will trigger change
    expect(spy).toHaveBeenCalledTimes(1);
});

Comments

[malvadao]

component.searchForm.controls['your_input'].setValue('test') this has successfully triggered the valueChange. Thank you!