在构造函数

Question

我正在努力对构造函数中具有异步Http调用的Angular2服务进行单元测试（现在我想知道它应该首先在这里）。

下面的示例代码 - 模拟的调用似乎永远不会被执行，我不知道我应该把它放在哪里。测试失败，因为我声明的属性在执行时是未定义的。我尝试使用fakeAsync和tick（）但是它们都没有用。

服务类：

    @Injectable
    export class Service {

      private data: any; //some object that will be returned from server

      constructor(private http: Http) {
                    this.http.get('url')
                      .map( (res: Response) => res.json())
                      .subscribe(res => this.data = res);
                  }
      getId() {
         return data.id;
      }

    }

单元测试：

describe('service test...', () => {

    let service: Service;
    let backend: MockBackend;
    let result = { id: 123 };

    beforeEach(() => {

        TestBed.configureTestingModule({
            imports: [HttpModule],
            providers: [
                Service,
                {
                    provide: Http,
                    useFactory: (mockBackend, options) => {
                        return new Http(mockBackend, options);
                    },
                    deps: [MockBackend, BaseRequestOptions]
                },
                MockBackend,
                BaseRequestOptions
            ]
        });

    });

    beforeEach(inject([Service, MockBackend], (s, mb) => {
        service = s;
        backend = mb;

        backend.connections.subscribe((conn) => {
            conn.mockRespond(new Response(new ResponseOptions({body: result})));
        });
    }));

    describe('test...', () => {

        it('should have id of 123...', async(() => {
            expect(service.getId()).toEqual(123);
        }));

    });

});