ngX异步断言没有得到正确的期望

Question

无论我在异步断言中的期望是什么，测试总是通过。此外，在console.log语句后调用then时，不会显示任何日志。我的代码如下所示..

import { TestBed, async } from '@angular/core/testing'
import { RouterTestingModule } from '@angular/router/testing'
import { HttpModule, XHRBackend } from '@angular/http'
import { MockBackend } from '@angular/http/testing'
import { ApiService } from '../../client/services/api.service '
import { SocketService } from '../../client/services/socket.service'
import { EventService } from '../../client/services/event.service'
import { DirectMessageComponent } from '../../client/components/messages/direct.component'
import { SharedModule } from '../../client/components/common/shared.module'

describe('DirectMessageComponent', () => {
  // High order variables
  let comp
  let fixture

  // Asynchronous beforeEach
  beforeEach(async(() => {
    // Configure the test bed
    TestBed.configureTestingModule({
      imports: [ SharedModule, HttpModule, RouterTestingModule ],
      declarations: [ DirectMessageComponent ],
      providers: [
        ApiService,
        SocketService,
        EventService,
        { provide: XHRBackend, useClass: MockBackend }
      ]
    })
    .compileComponents() // compile template and css
  }))

  // Synchronous beforeEach
  beforeEach(() => {
    // Assignments
    fixture = TestBed.createComponent(DirectMessageComponent)
    comp = fixture.componentInstance

    // Detect changes which fires ngOnInit
    fixture.detectChanges()
  })

  it('should get messages', async(() => {
    fixture.whenStable()
      .then(() => {
        expect(comp.message.length).toBeGreaterThan(0)
      })
  }))

})

有趣的是，即使正确调用fakeAsync，使用tick()方法执行也会失败。