如何使用可观察服务测试组件错误处理

Question

上下文

我正在尝试测试一个组件。在另一篇文章中，我询问了有关测试直接函数调用的问题。在这里，我使用相同的示例组件将重点放在组件的错误处理上。

我想测试，当我的服务返回一个可观察到的错误时，我的组件是否正确调用了 console.error(error)。

如何“创建”此错误触发器并测试我的组件是否正确处理它。我听说间谍可以做到这一点，但我不知道在哪里设置这个间谍。

我想模拟服务上的http请求可能失败的情况。出于任何原因或任何错误代码。

代码

这是组件、存根服务和我的规范文件的代码。

组件

import { Component, OnInit, ViewContainerRef } from '@angular/core';

import { UserManagementService } from '../../shared/services/global.api';
import { UserListItemComponent } from './user-list-item.component';

@Component({
  selector: 'app-user-list',
  templateUrl: './user-list.component.html'
})
export class UserListComponent implements OnInit {
  public userList = [];

  constructor(
    private _userManagementService: UserManagementService,    
  ) { }

  ngOnInit() {
    this.getUserList();
  }

  onRefreshUserList() {
    this.getUserList();
  }

  getUserList(notifyWhenComplete = false) {
    this._userManagementService.getListUsers().subscribe(
      result => {
        this.userList = result.objects;
      },
      error => {
        console.error(error); // That's the part of my component I want to test     
      },
      () => {
        if (notifyWhenComplete) {
          console.info('Notification');
        }
      }
    );
  }
}

组件规格文件

import { NO_ERRORS_SCHEMA } from '@angular/core';
import {
  async,
  fakeAsync,
  ComponentFixture,
  TestBed,
  tick,
  inject
} from '@angular/core/testing';

import { Observable } from 'rxjs/Observable';

// Components
import { UserListComponent } from './user-list.component';

// Services
import { UserManagementService } from '../../shared/services/global.api';
import { UserManagementServiceStub } from '../../testing/services/global.api.stub';

let comp:    UserListComponent;
let fixture: ComponentFixture<UserListComponent>;
let service: UserManagementService;

describe('UserListComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [UserListComponent],
      imports: [],
      providers: [
        {
          provide: UserManagementService,
          useClass: UserManagementServiceStub
        }
      ],
      schemas: [ NO_ERRORS_SCHEMA ]
    })
    .compileComponents();
  }));

  tests();
});

function tests() {
  beforeEach(() => {
    fixture = TestBed.createComponent(UserListComponent);
    comp = fixture.componentInstance;

    service = TestBed.get(UserManagementService);
  });

  it(`should be initialized`, () => {
    expect(fixture).toBeDefined();
    expect(comp).toBeDefined();
  });

  it(`should get the user List after ngOnInit`, async(() => {
    fixture.detectChanges();

    expect(comp.userList.length).toBe(3, 'user list exists after init');
  }));
}

存根服务

import { Observable } from 'rxjs/Observable';

export class UserManagementServiceStub {
  getListUsers() {
    return Observable.from([      
      {
        count: 3, 
        objects: 
        [
          {
            id: "7f5a6610-f59b-4cd7-b649-1ea3cf72347f",
            name: "user 1",
            group: "any"
          },
          {
            id: "d6f54c29-810e-43d8-8083-0712d1c412a3",
            name: "user 2",
            group: "any"
          },
          {
            id: "2874f506-009a-4af8-8ca5-f6e6ba1824cb", 
            name: "user 3",
            group: "any"
          }
        ]
      }
    ]);
  }
}

Answer 1

如果我的理解是正确的，您只需要一种从存根服务返回错误的方法，您可以创建一个单独的存根来返回一个可观察的错误，然后在检查错误处理的测试中使用它：

export class UserManagementServiceErrorStub {
  getListUsers() {
    return Observable.throw(new Error('Test error'));
  }
}

这里有一篇关于使用 Observables 测试 Angular 服务的非常好的文章： https://web.archive.org/web/20191214083526/http://www.zackarychapple.guru/angular2/2016/11/25/angular2-testing-services.html

更新 - RxJS 6 的 01/06/2019

import { throwError } from 'rxjs'; 

class UserManagementServiceErrorStub {
  getListUsers() {
    return throwError(new Error('Test error'));
  }
}