如何为异步方法编写单元测试？

Question

我有以下测试代码：

import {HttpClientTestingModule, HttpTestingController} from '@angular/common/http/testing';
import {inject, TestBed} from '@angular/core/testing';
import {AviorBackendService} from './avior-backend.service';

describe('AviorBackendService', () => {
  beforeEach(() => TestBed.configureTestingModule({
    imports: [HttpClientTestingModule],
    providers: [AviorBackendService],
  }));

  it('should be created', () => {
    const service: AviorBackendService = TestBed.get(AviorBackendService);
    expect(service).toBeTruthy();
  });

  // Inject the `done` method. This will tell the test suite that asynchronous methods are being called
  // and it will mark the test as failed if within a specific timeout (usually 5s) the `done` is not called
  it('expects service to fetch data with proper sorting', (done) => {
    const service: AviorBackendService = TestBed.get(AviorBackendService);
    // tslint:disable-next-line: prefer-const
    let httpMock: HttpTestingController;
    service.getUserCollection().subscribe(data => {
      expect(data.length).toBe(7);
      const req = httpMock.expectOne('http://localhost:3000/users');
      expect(req.request.method).toEqual('GET');      // Then we set the fake data to be returned by the mock
      req.flush({firstname: 'Chad'});
      done(); // Mark the test as done
    }, done.fail); // Mark the test as failed if something goes wrong
  });
});

我需要为提供的功能编写一个原型测试（然后，其余的将为其他类似的功能编写）。我仍在学习如何编写测试，据我所知，我需要使用模拟程序，但我不知道如何使用。我要测试的代码是：

  getUserCollection() {
    // withCredentials is very important as it passes the JWT cookie needed to authenticate
    return this.client.get<User[]>(SERVICE_URL + 'users', { withCredentials: true });
  }

我的测试代码给出错误Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.

Answer 1

您在错误的位置（永远不会被走过的地方）使用flush。

尝试以下操作：

describe('AviorBackendService', () => {
  let httpTestingController: HttpTestingController;
  let service: AviorBackendService;

  beforeEach(() => {
   TestBed.configureTestingModule({
     imports: [HttpClientTestingModule],
     providers: [AviorBackendService],
   });

   httpTestingController = TestBed.get(HttpTestingController);
   service = TestBed.get(AviorBackendService);
  });

  it('should be created', () => {
    expect(service).toBeTruthy();
  });

  it('expects the service to fetch data with proper sorting', () => {
    const mockReponse = { firstName: 'Chad' };

    service.getUserCollection().subscribe(data => {
      expect(data.firstName).toEqual('Chad');
    });
    const req = httpTestingController.expectOne('IN HERE PUT WHATEVER SERVICE_URL + 'users' EQUALS TO');
    expect(req.request.method).toEqual('POST');
    // send the response to the subscribe.
    req.flush(mockResponse);
  });
});

有关如何在Angular中测试HTTP服务（https://medium.com/better-programming/testing-http-requests-in-angular-with-httpclienttestingmodule-3880ceac74cf）的良好链接