Exploring Angular Testing with SpyOn

Apologies for my inexperience with Angular, but I am struggling with using spyOn in a unit test.

In my unit test, there is a method on the component that calls service1, which in turn calls another service2.

However, when I try to spyOn service1 in order to use a mock value, it ends up calling the actual ServiceProvidersHTTPService.getAllUsers instead of MockAppConfigService as intended.

Below is an excerpt from my Test:

describe('ProjectAnalystComponent', () => {
  let component: ProjectAnalystComponent;
let fixture: ComponentFixture<ProjectAnalystComponent>;
let service: ServiceProvidersHTTPService ;

  beforeEach(async(() => {
TestBed.configureTestingModule({
  imports: [HttpClientModule, RouterTestingModule],
    declarations: [ ProjectAnalystComponent ],
  providers: 
  [
    ServiceProvidersHTTPService, 
    CurrentCreateProjectService, 
    NotificationService, 
    MessageService,
    ProjectLeadAnalystHTTPService,
      ExceptionService,
      {provide: AppConfigService, useClass: MockAppConfigService }

  ],
  schemas: [CUSTOM_ELEMENTS_SCHEMA, NO_ERRORS_SCHEMA]
})
.compileComponents();
  }));

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

it('should create', () => {
    console.log("######### Did this run");
    let service = fixture.debugElement.injector.get(ServiceProvidersHTTPService);
    spyOn(service, 'getAllUsers').and.returnValue('{}');

    expect(component).toBeTruthy();
  });
});

Answer №1

TL;DR Utilize mock services.

Explanation

When setting up your testbed, you can either use the actual service :

providers:[ServiceProvidersHTTPService, ...

This involves calling the real methods of your service.

Alternatively, if you decide to mock your service like this :

{provide: AppConfigService, useClass: MockAppConfigService }

You will then call random functions specified in your mock.

An added benefit of mocking is that it helps eliminate dependencies on other services.

For example, if your service relies on another service: by mocking the first service, you don't need to include the dependencies of that service in your testbed.

The recommended method is as follows:

const mock = {
  provide: ServiceProvidersHTTPService,
  useValue: {
    getAllUsers: () => null
  }
};

Incorporate the mock in your testbed now:

providers: [mock, ...

Ensure that in useValue, you define all the variables and functions of your original service, and mock them accordingly.

For instance, instead of executing HTTP requests, the function getAllUsers will simply return null. You have the flexibility to make it return any desired value (it's best to return a value of the same type expected).

A final piece of advice: focus your unit tests on the functions and methods of your primary feature (in this case, ProjectAnalystComponent). Reserve testing the interaction with other services for the respective unit tests of those services.

If you have any inquiries, don't hesitate to ask!

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