Conas a dhéanann tú tástáil ar chomhpháirteanna agus seirbhísí Angular?

Question

Accepted Answer

Loiceann Angular tacar iomlán tástála (Jasmine + Karma de réir réamhshocraithe, cé go n-úsáideann go leor foirne Jest). Soláthraíonn sé **`TestBed`** chun modúl tástála a chumrú agus comhpháirteanna/seirbhísí a thiomsú le a gcuid spleáchais — ag úsáid DI chun fáillithe a instealladh.

## 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
  });
});
```

Ligann `HttpClientTestingModule` + `HttpTestingController` duit iarratais a dhearbhú agus freagraí bréige a sholáthar gan dul i ngleic le fíor-fhreastalaí.

## 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
  });
});
```

Tugann an `ComponentFixture` rochtain ar an sampla comhpháirte **agus** ar a DOM rindreáilte; ní mór duit `fixture.detectChanges()` a ghlaoch chun breatú ar athruithe a rith tar éis idirgníomhaithe.

## Mocking dependencies via DI

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

Déanann DI Angular an gréim a bheith fánach — soláthraigh cur i bhfeidhm bréige d'aon spleáchais.

## Async testing

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

Rialaíonn `fakeAsync`/`tick` (nó `waitForAsync`) am asincronach ar bhealach dinntithe.

## 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
```

## Cén fáth a bhí sé tábhachtach

Is ábhar ar an chéad sprioc tástála in Angular, agus fágann a dheilbhíocht DI go háirithe testable iad — insteallánn tú fáillithe d'aon spleáchais.

A bheith ar an eolas faoi `TestBed` (cumrú + instealladh), `ComponentFixture` (sampla + DOM + `detectChanges`), `HttpClientTestingModule` do HTTP, agus cabhraithe asincronach (`fakeAsync`/`tick`) clúdaíonn sé tástálacha aonad agus comhtháthaithe iontaofa a scríobh — riachtanach do na feidhmchláir fhada, fada mhóra feidhmchláir a bhuildíodh Angular dó.