Kako testirate Angular komponente i servise?

Question

Accepted Answer

Angular isporučuje kompletan test setup (Jasmine + Karma po zadanim postavkama, iako mnogi timovi koriste Jest). Pruža **`TestBed`** za konfiguriranje test modula i instanciranje komponenti/servisa sa njihovim ovisnostima — koristeći DI za ubacivanje mock-ova.

## Testing a service (simplest)

```ts
describe("UserService", () => {
  let service: UserService;
  let httpMock: HttpTestingController;

beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule], // mock HttpClient
      providers: [UserService],
    });
    service = TestBed.inject(UserService);
    httpMock = TestBed.inject(HttpTestingController);
  });

it("fetches users", () => {
    service.getUsers().subscribe(users => expect(users.length).toBe(2));
    const req = httpMock.expectOne("/api/users"); // assert the request was made
    req.flush([{ id: 1 }, { id: 2 }]);             // provide a fake response
  });
});
```

`HttpClientTestingModule` + `HttpTestingController` omogućuju vam da potvrdite zahtjeve i dodate lažne odgovore bez da pogodite pravi server.

## Testing a component

```ts
describe("CounterComponent", () => {
  let fixture: ComponentFixture<CounterComponent>;
  let component: CounterComponent;

beforeEach(() => {
    TestBed.configureTestingModule({ imports: [CounterComponent] }); // standalone
    fixture = TestBed.createComponent(CounterComponent);
    component = fixture.componentInstance;
    fixture.detectChanges(); // trigger initial change detection
  });

it("increments on click", () => {
    const button = fixture.nativeElement.querySelector("button");
    button.click();
    fixture.detectChanges();                     // update the view
    expect(component.count).toBe(1);
    expect(button.textContent).toContain("1");   // assert the rendered DOM
  });
});
```

`ComponentFixture` daje pristup instanci komponente **i** njenoj rendiranome DOM-u; morate pozvati `fixture.detectChanges()` da biste pokrenuli detekciju promjena nakon interakcija.

## Mocking dependencies via DI

```ts
TestBed.configureTestingModule({
  providers: [{ provide: AuthService, useValue: mockAuthService }], // inject a fake
});
```

Angular-ov DI čini mock-iranje trivijalno — pruža lažnu implementaciju za bilo koju ovisnost.

## Async testing

```ts
it("loads async", fakeAsync(() => {
  component.load();
  tick();                  // simulate passage of time / flush microtasks
  fixture.detectChanges();
  expect(component.data).toBeDefined();
}));
```

`fakeAsync`/`tick` (ili `waitForAsync`) determinističko kontroliraju asinkroni timing.

## Testing levels

```text
Unit:        services, pipes, isolated component logic (fast, most numerous)
Integration: component + template + child components via TestBed
E2E:         full user flows (Cypress, Playwright) — separate from unit tests
```

## Zašto je to važno

Testiranje je prvi razred briga u Angular-u, a njegova DI arhitektura čini ga posebno testabilnim — injicirate mock-ove za bilo koju ovisnost.

Znanje `TestBed` (configure + inject), `ComponentFixture` (instance + DOM + `detectChanges`), `HttpClientTestingModule` za HTTP i async pomoćnika (`fakeAsync`/`tick`) pokriva pisanje pouzdanih unit i integracijskih testova — esencijalno za velike, dugoročne enterprise aplikacije za koje je Angular sagrađen.