如何在 Angular 组件中模拟服务功能以进行单元测试

Question

我正在为 Angular 应用程序编写单元测试，我正在测试服务函数是否返回值。

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;
   }
}

我相信我已经在我的测试中模拟了服务功能，所以我希望它必须到达变量设置为“真”的其他部分。

TopToolBarService.ts

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

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

  getCustomer() {
    return this.customer;
  }
}

Answer 1

您必须在运行代码之前配置测试模块。它不知道您的间谍对象，除非您将其作为导入传递给TestBed.configureTestingModule。

https://angular.io/guide/testing#component-with-a-dependency

Answer 2

尝试在 beforeEach(async(() => ...) 中更新提供程序并将您的 mockedService 变量移到它的顶部：

describe('Component TEST', () => {
   ...
   let mockToolBarService;
   ...
      beforeEach(async(() => {
      ...
      mockToolBarService = jasmine.createSpyObj(['getCustomer']);
      mockToolBarService.getCustomer.and.returnValue('king');
      TestBed.configureTestingModule ({
           ...
           providers: [ { provide: TopToolBarService, useValue: mockToolBarService } ]
           ...

希望对你有帮助！

Answer 3

更改您的提供者值

beforeEach(() => {
   TestBed.configureTestingModule({
      declarations: [ UsersListComponent],
      providers: [{
         provide: TopToolBarService,
         useValue: jasmine.createSpyObj('TopToolBarService', ['getCustomer'])
      }],
      schemas:[CUSTOM_ELEMENTS_SCHEMA]
     });
     mockTopToolBarService = TestBed.get(TopToolBarService);

     mockTopToolBarService.getCustomer.and.returnValue(of([])); // mock output of function
   })

Answer 4

您可以考虑使用ng-mocks 来避免使用所有样板来配置TestBed。

beforeEach(() => MockBuilder(UsersListComponent)
  .mock(TopToolBarService, {
    // adding custom behavior to the service
    getCustomer: jasmine.createSpy().and.returnValue('king'),
  })
);

it('should return data from service function', () => {
  const fixture = MockRender(UsersListComponent);
  // now right after the render the property should be true
  expect(fixtur.point.componentInstance.bDefine).toBe(true);
}));

Answer 5

@Pedro Bezanilla 的回答已经足够好了。鉴于服务是单例的，我认为这是大多数情况下的另一种代码更少的方式。

不同之处在于configureTestingModule 没有提供提供程序配置。间谍是由 spyOn 针对从 TestBed 获取的服务对象设置的。

调用 TestBed.inject 而不是 TestBed.get 是因为它自 v9.0.0 以来已被弃用。

对于单例服务，这里是a doc in Angular website，为了完成，请记住this GitHub issue。

describe('Component TEST', () => {
  ...
  let mockToolBarService: TopToolBarService;
  ...
  beforeEach(waitForAsync(() => {
    TestBed.configureTestingModule({
      declarations: [ UsersListComponent ],
      schemas:[ CUSTOM_ELEMENTS_SCHEMA ]
    });
    mockTopToolBarService = TestBed.inject(TopToolBarService);
    spyOn(mockTopToolBarService, 'getCustomer').and.returnValue(of([]));
  }));
  ...