Angular4与AngularFire2单元测试失效求助，AngularfireDatabase同现问题

Hey there! Let's break down some common culprits that cause weird errors when testing Angular services (especially those using AngularFireDatabase) where dependencies are initialized in the constructor:

1. AngularFire Test Module Isn't Properly Configured #

If your test module doesn't import the necessary AngularFire modules or provide a valid (even mock) Firebase config, the service will fail to initialize properly—leading to vague dependency errors.

Here's how to set it up correctly, either with a mock config or a real one for integration tests:

beforeEach(() => {
  TestBed.configureTestingModule({
    imports: [
      // Initialize with a mock Firebase app config
      AngularFireModule.initializeApp({
        apiKey: "mock-key",
        authDomain: "mock-domain.firebaseapp.com",
        projectId: "mock-project"
      }),
      AngularFireDatabaseModule
    ],
    providers: [YourTargetService]
  });
});

For unit tests that don't need a real database, you can swap in the mock AngularFireDatabase from @angular/fire/mock:

providers: [
  YourTargetService,
  { provide: AngularFireDatabase, useClass: MockAngularFireDatabase }
]

2. Constructor Dependencies Are Missing or Unmocked #

If your service relies on other dependencies besides AngularFireDatabase, failing to provide mock instances or real implementations will trigger injection errors that might look "weird" at first glance.

For example, if your service uses an AuthService alongside AngularFireDatabase:

beforeEach(() => {
  TestBed.configureTestingModule({
    providers: [
      YourTargetService,
      // Mock AuthService with spy methods
      { provide: AuthService, useValue: jasmine.createSpyObj('AuthService', ['getCurrentUser']) },
      { provide: AngularFireDatabase, useClass: MockAngularFireDatabase }
    ]
  });
});

3. Async Initialization Isn't Handled #

If your service runs async operations (like subscribing to a Firebase database ref) directly in the constructor, tests might execute assertions before the async work completes—resulting in undefined values or unexpected states.

Use async/await or fakeAsync/tick to handle these timing issues:

// Using async/await
it('should load data on initialization', async () => {
  const service = TestBed.inject(YourTargetService);
  // Wait for async operations to resolve
  await new Promise(resolve => setTimeout(resolve, 0));
  expect(service.data).toBeDefined();
});

// Or using fakeAsync/tick
it('should load data on initialization', fakeAsync(() => {
  const service = TestBed.inject(YourTargetService);
  tick(); // Triggers all pending async tasks
  expect(service.data).toBeDefined();
}));

4. Duplicate Firebase App Initialization #

If you're running multiple test cases, you might hit a "Firebase app already exists" error if the app isn't cleaned up between tests. This can manifest as random-seeming failures.

Add cleanup logic in your beforeEach to avoid this:

beforeEach(() => {
  // Delete existing Firebase app if it exists
  if (firebase.apps.length > 0) {
    firebase.app('[DEFAULT]').delete();
  }
  
  TestBed.configureTestingModule({
    // Your module config here
  });
});

If none of these fix your issue, sharing the exact error message and snippets from your spec/service code would help narrow things down further!

内容的提问来源于stack exchange，提问作者coder