ReferenceError: Cannot access Service' before initialization

Question

Im getting an error when i run a unit test with jasmine on angular8 app. I have a service and inside this service im injecting another service

@Injectable({
  providedIn: 'root'
})

export class FirstService {
  constructor(private http: HttpClient, private configService: ConfigurationService) { }

when i do npm run test i always got an error:

An error was thrown in afterAll ReferenceError: Cannot access 'ConfigurationService' before initialization at Module.ConfigurationService (http://localhost:9876/_karma_webpack_/main.js:1095:112)

Any help?

Answer 1

You would need to provide a mock of ConfigService because it is a dependency of FirstService. The easiest way to do that is with a spy.

Something like:

let firstService: FirstServicec;
let configServiceSpy: jasmine.SpyObj<ConfigService>;

beforeEach(() => {
  const spy = jasmine.createSpyObj('ConfigService', ['getValue']);

  TestBed.configureTestingModule({
    providers: [
      FirstService,
      { provide: ConfigService, useValue: spy }
    ]
  });
  // Inject both the service-to-test and its (spy) dependency
  configService = TestBed.get(ConfigService);
  configServiceSpy = TestBed.get(ValueService);
});

Then, you can consume the spy in the test like:

it('#getValue should return stubbed value from a spy', () => {
  const stubValue = 'stub value';
  configServiceSpy.getValue.and.returnValue(stubValue);

  expect(firstService.getValue())
    .toBe(stubValue, 'service returned stub value');
  expect(configServiceSpy.getValue.calls.count())
    .toBe(1, 'spy method was called once');
  expect(configServiceSpy.getValue.calls.mostRecent().returnValue)
    .toBe(stubValue);
});

For more information, check out this section of the Angular Docs

Answer 2

This can be a very misleading error message.

A circular dependency may be causing it, solve your circular dependencies!

You will not see a circular dependency warning when running 'npm run test', but you will get a warning when running 'npm run serve' or 'npm run build'.