mock Observable concatMap function inside Unit test (Angular 5)

Question

Edit: I figured it out, the problem is spyOn will make the function it spy on to return undefined, need to call and.callThough explicitly.

I'm trying to test my component, which uses ngrx store. I'm stubbing my store in that unit test like this:

meetup-view.component.spec.ts

class ActivatedRouteStub {
  private subject = new Subject();

  push(value) {
    this.subject.next(value);
  }

  get params() {
    return this.subject.asObservable();
  }
}

class StoreStub {
  storeState = {
    auth: Observable.of({}),
    meetups: Observable.of([{key: '1'}])
  };

  select(value) {
    return this.storeState[value];
  }

  dispatch() {

  }
}

describe('MeetupCreateComponent', () => {
  let component: MeetupCreateComponent;
  let fixture: ComponentFixture<MeetupCreateComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [FormsModule],
      declarations: [ MeetupCreateComponent ],
      providers: [
        { provide: ActivatedRoute, useClass: ActivatedRouteStub },
        { provide: Store, useClass: StoreStub }
      ]
    })
    .compileComponents();
  }));

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

  it('should create', () => {
    expect(component).toBeTruthy();
  });

  it('should init edit/view mode correctly', () => {
    const route: ActivatedRouteStub = TestBed.get(ActivatedRoute);
    const store: StoreStub = TestBed.get(Store);
    const spy = spyOn(store, 'select').and.callThrough();
    route.push({id: 1});
    expect(spy).toHaveBeenCalled();
    expect(component.editMode).toBe(true);
  });
});

the problem is, in my component, I use concatMap (and import it using import 'rxjs/add/operator/concatMap';)

meetup-view.component.ts

this.meetup$ = this.store.select('meetups')
        .concatMap(meetups => {
          return meetups.filter(m => m.key === key);
        });

and when I run my unit test, I always get this error: Cannot read property 'concatMap' of undefined. I already tried to import concatMap to my unit tests but no luck. Been searching for hours now :(.