Angular 8 karma 测试服务而不在构造函数中注入所有服务

如何解决Angular 8 karma 测试服务而不在构造函数中注入所有服务

我是使用 Karma 进行 Angular 测试的新手，我不了解如何正确测试服务。假设我有这项服务需要测试：

    @Injectable()
    export class MyService {
        constructor(private httpService: HttpService) { }

        //methods to test
    }

这是我的测试课：

    describe('MyService',() => {
      let service: MyService;
      beforeEach(async(() => {
        Testbed.configureTestingModule({
          providers: [MyService],}).compileComponents();
        service = Testbed.get(MyService);
      }));
    });

当我运行 ng test 时，它给出了错误 NullInjectorError: No provider for HttpService!。
所以我在测试类中将 HttpService 添加到 providers 数组中，这样：

    describe('MyService',() => {
      let service: MyService;
      beforeEach(async(() => {
        Testbed.configureTestingModule({
          providers: [MyService,HttpService],}).compileComponents();
        service = Testbed.get(MyService);
      }));
    });

HttpService 是这样的：

    @Injectable()
    export class HttpService{
        constructor(private httpService: HttpClient) { }
    }

所以现在我收到错误 NullInjectorError: No provider for HttpClient!。（HttpClient 来自@angular/common/http）。
如果我将 HttpClient 添加到测试类中的 providers 数组，那么对于 HttpClient 构造函数中的所有服务/类，我都会收到相同的错误，依此类推。什么是实例化服务的正确方法，而不必添加每个提供者，从而导致潜在的无限提供者？

解决方法

在您的测试平台配置中，导入 HttpClientTestingModule

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],providers: [MyService,HttpService],}).compileComponents();
    service = TestBed.get(MyService);
  }));

你也可以考虑

将 TestBed.get(MyService); 更改为 TestBed.inject(MyService); 作为 TestBed.get(...) 已弃用 What's the difference between TestBed.get and new Service(...dependencies)
将 async 更改为 waitForAsync 作为 async 已弃用 When to use waitForAsync in angular

您应该使用 HttpClientTestingModule 并通过 HttpTestingController 和 flush 方法模拟数据。这是一个关于我如何测试服务的 Angular 11 和 jasmine 3.6.0 示例。希望能帮到你：

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

// Assets
import { ExampleService } from './api/example.service';

describe('*[Example Service]: -----------------------------------------',() => {
    let httpTestingController: HttpTestingController;
    let service: ExampleService;

    beforeEach(waitForAsync(() => {
        TestBed.configureTestingModule({
            imports: [
             HttpClientTestingModule
            ]
        }).compileComponents();
        
      httpTestingController = TestBed.inject(HttpTestingController);
      service = TestBed.inject(ExampleService);
    }));
    
    it('1). should get data from GET service',waitForAsync( () => {
      // Arrange
      const expectedData: string[] = ['data1','data2'];
      let apiError,apiData;
      // Action
      service.getData().subscribe(response => {
        apiData = response;
      },error => {
        apiError = error;
      });
      const request = httpTestingController.expectOne(`http://localhost:3000/example`);
      request.flush(expectedData);
      // Assert
      expect(apiData.length).toEqual(2);
      expect(apiError).toBeUndefined();
        }));

});