Angular 5 服务无法通过单元测试(NullInjectorError : No provider for HttpClient!)

Question

我在运行单元测试时不断收到以下错误

Error: StaticInjectorError(DynamicTestModule)[ApiService -> HttpClient]: 
      StaticInjectorError(Platform: core)[ApiService -> HttpClient]: 
        NullInjectorError: No provider for HttpClient!

api.service.ts

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable()
export class ApiService {

  constructor(private http: HttpClient) { }
  url = './assets/data.json';

  get() {
    return this.http.get(this.url);
  }
}

api.service.spec.ts

import { TestBed, inject } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';

import { ApiService } from './api.service';

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

  it('should get users', inject([HttpTestingController, ApiService],
      (httpMock: HttpTestingController, apiService: ApiService) => {
        expect(apiService).toBeTruthy();
      }
    )
  );
});

我不明白哪里出了问题，因为我已将 HttpClient 包含到 api.service.ts 中，该服务在浏览器中运行。

这个是在一个叫做MapComponent的组件中直接调用的，那个是在HomeComponent内部调用的。

Chrome 63.0.3239 (Mac OS X 10.13.3) HomeComponent expect opened to be false FAILED
    Error: StaticInjectorError(DynamicTestModule)[ApiService -> HttpClient]: 
      StaticInjectorError(Platform: core)[ApiService -> HttpClient]: 
        NullInjectorError: No provider for HttpClient!

Answer 1

"NullInjectorError: No provider for HttpClient!" 的原因是 Unresolved 依赖项。在这种情况下，缺少 HttpClientModule。

在你的 .service.spec.ts 文件中添加

  imports: [
        HttpClientTestingModule,
    ],

您可能会注意到我写的是 HttpClientTestingModule 而不是 HttpClientModule。原因是我们不想发送实际的 http 请求，而是使用测试框架的 Mock API。