Unit Test

Mocking

• Use mocks for all dependencies, instead of the real dependencies.
• Recommend to use ng-mocks to quickly mock up dependencies.
• Use ng-mocks together with Jest to customize mocking and spying for more complicated scenarios.

Anti-pattern

• Avoid testing the round-trip. Test only the isolated piece.

Scenarios

• Overwrite default mocking implementation within test: jest.spyon(myObject, 'someMethod').mockImplementation()
• Use fakeAsync and tick from Angular testing utilities to deal with asynchronous code.
• To test multiple subscriptions within ngOnInit, for each subscription, conditionally return a specific observable.

        jest.spyOn(dataService, 'sub').mockImplementationOnce((s, e) => {
        if (e === Events.ON_SUBMIT) {
          return of([1]); // Return an observable on Events.ON_SUBMIT event stream
        }
        return EMPTY; // Return an EMPTY on all other event streams
      });