Paano za ka bugi sassa Angular components da services?

Question

IT Interview Practice · Accepted Answer

Angular yana shiryar cikakken saitin bugi (Jasmine + Karma ta tsinkayi, kodayake da yawa jiha suna amfani da Jest). Yana ba da **`TestBed`** don saita modul bugi da aiwatar sassa/sabis tare da abubuwan da suka dogara — yin amfani da DI don saka ita sa magani.

## 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` suna ba ka damar tantance bukati da samar da amsosai mara ainihi ba tare da bugi ainihin sabar ba.

## 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` yana ba da damar zuwa sassan yatiyye **da** DOM na sa masa; dole ne ka kira `fixture.detectChanges()` don aiwatar bincike na sauyi bayan abubuwan da ake aiki.

## Mocking dependencies via DI

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

Angular's DI yana sa ita sa magani mai sauki — samar da aiwatarwa ta ita sa magani ga kowane baban abubuwan da ake taba wa shi.

## Async testing

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

`fakeAsync`/`tick` (ko `waitForAsync`) suna himma matsanancin lokaci ta sauki da gumaka.

## 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
```

## Me ya sa yana mahimmanci

Bugi ne babbar batu a Angular, kuma tsarin DI na sa a lissafi - ka saka ita sa magani ga kowane babban batu.

Sanin `TestBed` (configure + inject), `ComponentFixture` (instance + DOM + `detectChanges`), `HttpClientTestingModule` don HTTP, da abubuwan taimako na asunkewa (`fakeAsync`/`tick`) yana ɗora rubuta bugun imani da haɗa - mahimmanci ne don manyan aikace-aikace na kamshekoli na dogon waji Angular aka gina shi.

Testing a service (simplest)

Testing a component

Mocking dependencies via DI

Async testing

Testing levels

Me ya sa yana mahimmanci

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