Angular 2 错误：Karma-Jasmine 测试中没有 Http 提供者

Question

即使我的应用程序运行良好且没有错误，我仍然在我的业力测试中收到以下错误。就是说没有 Http 的提供者。我在 app.module.ts 文件中使用 import { HttpModule } from '@angular/http'; 并将其添加到导入数组中。业力错误如下所示：

Chrome 52.0.2743 (Mac OS X 10.12.0) App: TrackBudget should create the app FAILED
    Failed: Error in ./AppComponent class AppComponent_Host - inline template:0:0 caused by: No provider for Http!
    Error: No provider for Http!
        at NoProviderError.Error (native)
        at NoProviderError.BaseError [as constructor] (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/facade/errors.js:24:0 <- src/test.ts:2559:34)
        at NoProviderError.AbstractProviderError [as constructor] (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_errors.js:42:0 <- src/test.ts:15415:16)
        at new NoProviderError (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_errors.js:73:0 <- src/test.ts:15446:16)
        at ReflectiveInjector_._throwOrNull (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_injector.js:761:0 <- src/test.ts:26066:19)
        at ReflectiveInjector_._getByKeyDefault (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_injector.js:789:0 <- src/test.ts:26094:25)
        at ReflectiveInjector_._getByKey (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_injector.js:752:0 <- src/test.ts:26057:25)
        at ReflectiveInjector_.get (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/src/di/reflective_injector.js:561:0 <- src/test.ts:25866:21)
        at TestBed.get (webpack:/Users/ChrisGaona%201/budget-tracking/~/@angular/core/bundles/core-testing.umd.js:1115:0 <- src/test.ts:5626:67)
Chrome 52.0.2743 (Mac OS X 10.12.0): Executed 1 of 1 (1 FAILED) ERROR (0.229 secs / 0.174 secs)

这是我的 app.component.ts 文件：

import {Component} from '@angular/core';
import {Budget} from "./budget";
import {BudgetService} from "./budget.service";

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css'],
    providers: [BudgetService]
})
export class AppComponent {
    title = 'Budget Tracker';

    budgets: Budget[];
    selectedBudget: Budget;

    constructor(private budgetService: BudgetService) { }

    ngOnInit(): void {
        this.budgetService.getBudgets()
            .subscribe(data => {
                this.budgets = data;
                console.log(data);
                this.selectedBudget = data[0];
                console.log(data[0]);
            });
    }
}

这是我的简单规范：

import { TestBed, async } from '@angular/core/testing';
import { AppComponent } from './app.component';

describe('App: TrackBudget', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
        declarations: [
            AppComponent
        ]
    });
  });

  it('should create the app', async(() => {
    let fixture = TestBed.createComponent(AppComponent);
    let app = fixture.debugElement.componentInstance;
    expect(app).toBeTruthy();
  }));
});

错误似乎是我的服务造成的，可以看这里：

import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
import 'rxjs/add/operator/map';
import {Budget} from "./budget";

@Injectable()
export class BudgetService {

  constructor(public http: Http) { }

  getBudgets() {
    return this.http.get('budget.json')
        .map(response => <Budget[]>response.json().budgetData);

  }
}

如果我从服务中删除 constructor(public http: Http) { } 语句，则测试可以正常通过，但是应用程序在浏览器中失败。我对此进行了很多研究，但无法找出解决方案。任何帮助将不胜感激！

Answer 1

注意：此解决方案仅在您想测试静态结构时才有效。如果您的测试确实进行了服务调用（并且您最好也进行其中一些测试），那么它将无法正常工作。

您的测试使用自己的模块定义、测试模块，而不是您的 AppModule。所以你也必须在那里导入 HttpModule：

TestBed.configureTestingModule({
    imports: [
        HttpModule
    ],
    declarations: [
        AppComponent
    ]
});

您也可以导入您的 AppModule：

TestBed.configureTestingModule({
    imports: [
        AppModule
    ]
});

这样做的好处是您不必在很多地方添加新的组件和模块。它更方便。另一方面，这不太灵活。您可能会在测试中导入比您希望的更多的内容。

此外，您的低级组件依赖于整个 AppModule。事实上，这是一种循环依赖，这通常是个坏主意。所以在我看来，你应该只对那些对你的应用程序非常重要的高级组件这样做。对于更多甚至可以重用的低级组件，您最好在测试规范中明确列出所有依赖项。

Answer 2

TestBed 的目的是为测试环境配置一个@NgModule从头开始。所以目前你只配置了AppComponent，而什么都没有（除了已经在@Component.providers中声明的服务。

我强烈建议您做的，而不是像在真实环境中那样尝试配置所有内容，而是模拟BudgetService。尝试配置 Http 并模拟它不是最好的主意，因为您希望在单元测试时尽可能保持外部依赖关系。

这就是你需要做的事情

1. 为BudgetService 创建一个模拟。我会查看this post。您可以扩展该抽象类，添加您的 getBudgets 方法

2. 您需要覆盖@Component.providers，如this post中所述

如果你真的只想使用真正的服务和Http，那么你需要准备好在MockBackend 上模拟连接。您不能使用真正的后端，因为它依赖于平台浏览器。例如，查看this post。我个人认为在测试组件时这不是一个好主意。在测试您的服务时，这是您应该这样做的时候。

Answer 3

在 app.module.ts 中导入 HttpModule 即可解决您的问题。

import { HttpModule } from '@angular/http';

@NgModule({
    imports: [HttpModule]
})
...

Answer 4

peeskillet's answer 中描述的模拟服务的替代方法是使用Mock Backend provided by angular。

API 文档包含以下示例：

import {Injectable, ReflectiveInjector} from '@angular/core';
import {async, fakeAsync, tick} from '@angular/core/testing';
import {BaseRequestOptions, ConnectionBackend, Http, RequestOptions} from '@angular/http';
import {Response, ResponseOptions} from '@angular/http';
import {MockBackend, MockConnection} from '@angular/http/testing';

const HERO_ONE = 'HeroNrOne';
const HERO_TWO = 'WillBeAlwaysTheSecond';

@Injectable()
class HeroService {
  constructor(private http: Http) {}

  getHeroes(): Promise<String[]> {
    return this.http.get('myservices.de/api/heroes')
        .toPromise()
        .then(response => response.json().data)
        .catch(e => this.handleError(e));
  }

  private handleError(error: any): Promise<any> {
    console.error('An error occurred', error);
    return Promise.reject(error.message || error);
  }
}

describe('MockBackend HeroService Example', () => {
  beforeEach(() => {
    this.injector = ReflectiveInjector.resolveAndCreate([
      {provide: ConnectionBackend, useClass: MockBackend},
      {provide: RequestOptions, useClass: BaseRequestOptions},
      Http,
      HeroService,
    ]);
    this.heroService = this.injector.get(HeroService);
    this.backend = this.injector.get(ConnectionBackend) as MockBackend;
    this.backend.connections.subscribe((connection: any) => this.lastConnection = connection);
  });

  it('getHeroes() should query current service url', () => {
    this.heroService.getHeroes();
    expect(this.lastConnection).toBeDefined('no http service connection at all?');
    expect(this.lastConnection.request.url).toMatch(/api\/heroes$/, 'url invalid');
  });

  it('getHeroes() should return some heroes', fakeAsync(() => {
       let result: String[];
       this.heroService.getHeroes().then((heroes: String[]) => result = heroes);
       this.lastConnection.mockRespond(new Response(new ResponseOptions({
         body: JSON.stringify({data: [HERO_ONE, HERO_TWO]}),
       })));
       tick();
       expect(result.length).toEqual(2, 'should contain given amount of heroes');
       expect(result[0]).toEqual(HERO_ONE, ' HERO_ONE should be the first hero');
       expect(result[1]).toEqual(HERO_TWO, ' HERO_TWO should be the second hero');
     }));

  it('getHeroes() while server is down', fakeAsync(() => {
       let result: String[];
       let catchedError: any;
       this.heroService.getHeroes()
           .then((heroes: String[]) => result = heroes)
           .catch((error: any) => catchedError = error);
       this.lastConnection.mockRespond(new Response(new ResponseOptions({
         status: 404,
         statusText: 'URL not Found',
       })));
       tick();
       expect(result).toBeUndefined();
       expect(catchedError).toBeDefined();
     }));
});

Answer 5

在 Angular 4+ 上

RC2C's answer 为我工作 :) 谢谢！

警告：这仅在您不真正调用您的服务时才有效。它仅在您想测试静态结构时才有效。

只是想为 Angular 版本 4（可能更高版本）添加它，您应该将 HttpClientModule 导入您的测试平台，使其看起来像这样：

import { HttpClientModule } from '@angular/common/http';


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

  it('should be created 2', inject([BuildingService], (service: BuildingService) => {
    expect(service).toBeTruthy();
  }));

}

注意：见顶部注意