如何使用AngularFireDatabase和Jasmine Spy/Mock测试Angular服务

// app.service.ts
import { Injectable } from '@angular/core';
import { AngularFireDatabase } from '@angular/fire/database';

@Injectable()
export class AppService {
  constructor(private db: AngularFireDatabase) {}

  getData(): Promise<any> {
    return this.db.object('/data').valueChanges().toPromise();
  }
}

// app.service.spec.ts
import { TestBed, async, fakeAsync, tick } from '@angular/core/testing';
import { AngularFireDatabase } from '@angular/fire/database';
import { AppService } from './app.service';

describe('AppService', () => {
  let service: AppService;
  let dbMock: jasmine.SpyObj<AngularFireDatabase>;

  beforeEach(async(() => {
    const dbSpy = jasmine.createSpyObj('AngularFireDatabase', ['object']);
    TestBed.configureTestingModule({
      providers: [
        AppService,
        { provide: AngularFireDatabase, useValue: dbSpy }
      ]
    });
    service = TestBed.inject(AppService);
    dbMock = TestBed.inject(AngularFireDatabase) as jasmine.SpyObj<AngularFireDatabase>;
  }));

  it('should get data from Firebase', fakeAsync(() => {
    const testData = { key: 'value' };
    dbMock.object.and.returnValue({ valueChanges: () => testData });

    let result: any;
    service.getData().then(data => result = data);
    tick();

    expect(result).toEqual(testData);
    expect(dbMock.object).toHaveBeenCalledWith('/data');
  }));
});