Angular测试如何防止ngOnInit调用直接测试方法

Question

上下文

我有一个组件。在其中，ngOnInit 函数调用组件的另一个函数来检索用户列表。我想做两个系列的tets：

• 首先测试 ngOnInit 是否正确触发并填充用户列表
• 第二次我想测试我的刷新函数，它也调用 getUserList()

当我调用 fixture.detectChanges() 时，使用 ngOnInit 触发器的第一个测试工作正常。

问题

我的问题是在测试刷新函数时：一旦我调用了 fixture.detectChanges()，ngOnInit 就会被触发，然后我无法知道我的结果来自哪里以及我的 refresh() 函数是否会被正确测试。

在我对refresh() 方法进行第二系列测试之前，有什么办法可以“删除”或“阻止”ngOnInit()，这样就不会在fixture.detectChanges() 上调用它？ p>

我试图查看overrideComponent，但它似乎不允许删除ngOnInit()。

或者在我的情况下，除了使用fixture.detectChanges 之外，还有什么方法可以检测到更改？

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);        
      },
      () => {
        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 NOT have any user in list before ngOnInit`, () => {
    expect(comp.userList.length).toBe(0, 'user list is empty before init');
  });

  it(`should get the user List after ngOnInit`, async(() => {
    fixture.detectChanges(); // This triggers the ngOnInit and thus the getUserList() method

    // Works perfectly. ngOnInit was triggered and my list is OK
    expect(comp.userList.length).toBe(3, 'user list exists after init');
  }));

  it(`should get the user List via refresh function`, fakeAsync(() => {
    comp.onRefreshUserList(); // Can be commented, the test will pass because of ngOnInit trigger
    tick();

    // This triggers the ngOnInit which ALSO call getUserList()
    // so my result can come from getUserList() method called from both source: onRefreshUserList() AND through ngOnInit().
    fixture.detectChanges(); 

    // If I comment the first line, the expectation is met because ngOnInit was triggered!    
    expect(comp.userList.length).toBe(3, 'user list after function call');
  }));
}

存根服务（如果需要）

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"
          }
        ]
      }
    ]);
  }
}

我的试炼

我尝试了一些“解决方法”，但我发现它有点......冗长而且可能有点矫枉过正！

例如：

it(`should get the user List via refresh function`, fakeAsync(() => {
    expect(comp.userList.length).toBe(0, 'user list must be empty');

    // Here ngOnInit is called, so I override the result from onInit
    fixture.detectChanges();
    expect(comp.userList.length).toBe(3, 'ngOnInit');

    comp.userList = [];
    fixture.detectChanges();
    expect(comp.userList.length).toBe(0, 'ngOnInit');

    // Then call the refresh function
    comp.onRefreshUserList(true);
    tick();
    fixture.detectChanges();

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

Answer 1

阻止生命周期挂钩 (ngOnInit) 被调用是错误的方向。该问题有两个可能的原因。要么测试不够隔离，要么测试策略错误。

Angular 指南相当 specific and opinionated on test isolation:

但是，使用不依赖于 Angular 的独立单元测试来探索应用程序类的内部逻辑通常会更有效率。此类测试通常更小，更易于阅读、编写和维护。

所以孤立的测试应该实例化一个类并测试它的方法

userManagementService = new UserManagementServiceStub;
comp = new UserListComponent(userManagementService);
spyOn(comp, 'getUserList');

...
comp.ngOnInit();
expect(comp.getUserList).toHaveBeenCalled();

...
comp.onRefreshUserList();
expect(comp.getUserList).toHaveBeenCalled();

独立测试有一个缺点 - 它们不测试 DI，而 TestBed 测试可以。根据观点和测试策略，孤立的测试可以被认为是单元测试，而TestBed测试可以被认为是功能测试。一个好的测试套件可以同时包含这两者。

在上面的代码中should get the user List via refresh function test 显然是一个功能测试，它将组件实例视为一个黑盒。

可以添加几个 TestBed 单元测试来填补空白，它们可能足够稳固，不会打扰孤立的测试（尽管后者肯定更精确）：

spyOn(comp, 'getUserList');

comp.onRefreshUserList();
expect(comp.getUserList).toHaveBeenCalledTimes(1);

...

spyOn(comp, 'getUserList');
spyOn(comp, 'ngOnInit').and.callThrough();

tick();
fixture.detectChanges(); 

expect(comp.ngOnInit).toHaveBeenCalled();
expect(comp.getUserList).toHaveBeenCalledTimes(1);

Answer 2

it(`should get the user List via refresh function`, fakeAsync(() => {
  let ngOnInitFn = UserListComponent.prototype.ngOnInit;
  UserListComponent.prototype.ngOnInit = () => {} // override ngOnInit
  comp.onRefreshUserList();
  tick();

  fixture.detectChanges(); 
  UserListComponent.prototype.ngOnInit = ngOnInitFn; // revert ngOnInit

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

Plunker Example

Answer 3

我个人更喜欢为每个测试取消组件 ngOnInit。

beforeEach(() => {
    UserListComponent.prototype.ngOnInit = () => {} ;
   ....
  });