angular - 引用错误 : Cannot access Service' before initialization

Question

当我在 angular8 应用程序上使用 jasmine 运行单元测试时出现错误。
我有一个服务，在这个服务中我正在注入(inject)另一个服务

@Injectable({
  providedIn: 'root'
})

export class FirstService {
  constructor(private http: HttpClient, private configService: ConfigurationService) { }

当我执行 npm run test 时，总是出现错误:

An error was thrown in afterAll ReferenceError: Cannot access 'ConfigurationService' before initialization at Module.ConfigurationService (http://localhost:9876/_karma_webpack_/main.js:1095:112)

有什么帮助吗？

Answer 1

您需要提供 ConfigService 的模拟。因为它是 FirstService 的依赖项.最简单的方法是使用 spy 。

就像是:

let firstService: FirstServicec;
let configServiceSpy: jasmine.SpyObj<ConfigService>;

beforeEach(() => {
  const spy = jasmine.createSpyObj('ConfigService', ['getValue']);

  TestBed.configureTestingModule({
    providers: [
      FirstService,
      { provide: ConfigService, useValue: spy }
    ]
  });
  // Inject both the service-to-test and its (spy) dependency
  configService = TestBed.get(ConfigService);
  configServiceSpy = TestBed.get(ValueService);
});

然后，您可以在测试中使用 spy ，例如:

it('#getValue should return stubbed value from a spy', () => {
  const stubValue = 'stub value';
  configServiceSpy.getValue.and.returnValue(stubValue);

  expect(firstService.getValue())
    .toBe(stubValue, 'service returned stub value');
  expect(configServiceSpy.getValue.calls.count())
    .toBe(1, 'spy method was called once');
  expect(configServiceSpy.getValue.calls.mostRecent().returnValue)
    .toBe(stubValue);
});

有关更多信息，请查看 Angular Docs 的此部分