How cant test Query, Mutation, Subscription services using Apollo Angular?

Question

I saw the examples of how testing apollo in angular works and basically only use the ApolloTestingModule to make the tests. And my test looks like:

Test suit

describe('CountriesService', () => {
  let countryService: CountriesService;
  let controller: ApolloTestingController;
  let scheduler: TestScheduler;
  let countries: any;

  beforeAll(() => {
    TestBed.configureTestingModule({
      imports: [ApolloTestingModule],
    });

    countries = [{ code: 'C1', phone: '500', name: 'Country' }];
    scheduler = new TestScheduler((actual, expected) => {
      expect(actual).toEqual(expected);
    });
    countryService = TestBed.inject(CountriesService);
    controller = TestBed.inject(ApolloTestingController);
  });

  test('should be created', () => {
    expect(countryService).toBeTruthy();
  });

  test('should return an array of countries', () => {
    countryService.watch().valueChanges.subscribe(console.log);

    const operation = controller.expectOne(COUNTRIES_GQL);
    operation.flush({ data: { countries } });

    controller.verify();
  });
});

Service

@Injectable({ providedIn: 'root' })
export class CountriesService {
  constructor(private apollo: Apollo) {}

  watch() {
    return this.apollo.watchQuery({
      query: COUNTRIES_GQL,
    });
  }
}

Problem

I want to use the approach of using Query, Mutation, Subscription service but with this approach the test doesn't work.

@Injectable({ providedIn: 'root' })
export class CountriesService extends Query<any> {
  document = COUNTRIES_GQL;
}

Error

● CountriesService › should return an array of countries

    TypeError: Cannot read property 'use' of undefined

      30 | 
      31 |   test('should return an array of countries', () => {
      32 |     countryService.watch().valueChanges.subscribe(console.log);
         |                    ^
      33 | 
      34 |     const operation = controller.expectOne(COUNTRIES_GQL);
      35 |     operation.flush({ data: { countries } });

For me the error makes sense because in the official implementation of Query class the methods fetch and watch are using the use method provided by Apollo service.

Questions

• Does an alternative to test this type of service provided by apollo?
• If I want to use this approach, I should test it as a basic service?

I wait for your answers

Answer 1

try to instance ur service and call it with the methode countryService.watch() then

countryService.watch().valueChanges.subscribe(console.log);

Answer 2

I was able to get it working using this approach mocking the service in providers (does not use AppolloTestingModule). Made a helper function graphQlServiceMock for reuse across all services.

TestBed.configureTestingModule({
  ...
  providers: [
    {
       provide: MyGQLService,
       useValue: graphQlServiceMock({ users: null }),
    },
  ]

})

export const graphQlServiceMock = (response: any) => ({
  watch: () => ({
    valueChanges: of({
      data: {
        ...response,
      },
      loading: false,
    }),
  }),
});

or without helper..

TestBed.configureTestingModule({
  ...
  providers: [
  {
    provide: MyGQLService,
    useValue: {
      watch: () => ({
        valueChanges: of({
          data: {
            users: null,
          },
          loading: false,
        }),
      }),
    },
  },
 ];
})