How to return a fake/stub value for a particular selector in ngrx/store testing?

Question

[Using angular and ngrx.]

I'm using jest and jest-marbles for testing a service. I'm using the store inside this service. The service depends on a boolean value from the store (isDisplayItems).

If it is true, only then the other functions inside the service works.

So I need to mock a value so that I can make it working. It will be possible only if I can provide a fake value like this.

jest.spyOn(mockStore.pipe(select(s => s.isDisplayItems))).and.returnValue(true)

The idea here is to return a fake/stub value for a particular selector, so that I can test service.

  it('should make items visible', () =>
  {
    jest.spyOn(mockStore.pipe(select(s => s.isDisplayItems))).and.returnValue(true)

  });

How can I achieve that?

This is my test bed setup

  beforeEach(() =>
  {
    TestBed.configureTestingModule({
      providers: [provideMockStore({ initialState }),],
    });
    service = TestBed.inject(FilterService);
    mockStore = TestBed.inject(MockStore);
  });

Answer 1

Please follow ngrx docs how to test them: https://ngrx.io/guide/store/testing#using-mock-selectors

There's mockStore.overrideSelector for that.

mockStore.overrideSelector(
  yourSelectorHere,
  valueYouWantToReturnAsResult
);

for example

mockStore.overrideSelector(
  currentUser,
  null,
);

this.store.select(currentUser).subscribe(console.log); // prints null.