如何在Angular组件中模拟服务功能以进行单元测试

我正在为angular应用编写单元测试，正在测试服务函数是否返回值.

I am writing unit test for angular app, I am testing if the service function returns a value.

component.spec.ts

import {TopToolBarService} from '../../top-toolbar/top-toolbar.service';

beforeEach(async(() => {
   TestBed.configureTestingModule ({
   declarations: [ UsersListComponent],
   providers: [TopToolBarService],//tried mocking service here,still test failed
   schemas:[CUSTOM_ELEMENTS_SCHEMA]
 })
  .compileComponents();
}));



beforeEach(() => {
    fixture = TestBed.createComponent(UserListComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });



  it('should return data from service function', async(() => {
    let mockTopToolBarService: jasmine.SpyObj<TopToolBarService>;
    mockTopToolBarService = jasmine.createSpyObj('TopToolBarService', ['getCustomer']);
    mockTopToolBarService.getCustomer.and.returnValue("king");
    fixture.detectChanges();
    expect(component.bDefine).toBe(true); //fails
  }))

component.ts

bDefine = false;
ngOnInit() {
 let customer = this.topToolBarService.getCustomer();
 if (customer == null) {
   bDefine = false;
 } else {
    bDefine = true;
   }
}

我相信我在测试中嘲笑了服务函数，因此我希望它必须到达变量设置为"true"的其他部分.

I believe I have mocked the service function in my test, so I expect it must have reached else part where variable is set to 'true'.

TopToolBarService.ts

import { EventEmitter, Injectable, Output } from "@angular/core";

@Injectable()
export class TopToolBarService {
customer = null;

  getCustomer() {
    return this.customer;
  }
}