How to mock service function in Angular component for unit test

问题

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;
   }
}

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;
  }
}

回答1:

Try updating providers inside beforeEach(async(() => ...) and moving your mockedService variable on the top of it:

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

Hope it helps!

回答2:

Change your provider value

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
   })

回答3:

You have to configure the testing module before you run your code. It doesn't know about your spy object unless you pass it to the TestBed.configureTestingModule as an import.

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

回答4:

You might consider usage of ng-mocks to avoid all that boilerplate to configure 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);
}));

来源：https://stackoverflow.com/questions/58331328/how-to-mock-service-function-in-angular-component-for-unit-test

标签

angular

typescript

unit-testing