Test chain depended services

Question

I want test some service AService, which has some dependencies BService, which is depended on another service e.x. CService. We have chain like dependencies:

AService --> BService --> CService

AService constructor:

constructor(
  private bService: BService
) {}

BService constructor:

constructor(
   private cService: CService
) {}

If I want test AService in my test file I should write something like this:

beforeAll(() => {
      injector = ReflectiveInjector.resolveAndCreate([
            AService,
            BService,
            CService,
        ]);

        service = injector.get(AService);
   });

and if I have too many services, which are chained each other I'll get too much boilerplate.

Is there any way to doesn't inject all chained services in my AService testing file?

qdivision · Accepted Answer · 2017-04-03T15:38:25.610

Ideally, actual dependencies should not be included when unit testing your code. Instead you should supply a mock serviceB and stub those dependencies.

    describe('AService', () => {
       beforeAll(() => {
          injector = ReflectiveInjector.resolveAndCreate([
              AService,
              {provide: BService, useClass: MockBService}
              ]);
          Aservice = injector.get(AService);
       });
    });


    class MockBService {
      // enter mock functions here that you want to invoke from Service A
      // this does not have dependency on Service C
    }

In your tests, you can spy on those calls to Service B and return whatever value you want.

   const BService = AService.injector.get(BService);
   spyOn(BService, 'someFunc').and.returnValue(1);

Test chain depended services

1 Answers1