测试时出现 NullInjectorError

Question

我在 Angular 12 中进行运行 ng 测试时遇到以下问题：

NullInjectorError: R3InjectorError(DynamicTestModule)[BaseURL -> BaseURL]: NullInjectorError: No provider for BaseURL! error properties: Object({ ngTempTokenPath: null, ngTokenPath: [ 'BaseURL', 'BaseURL' ] }) NullInjectorError: R3InjectorError(DynamicTestModule)[BaseURL -> BaseURL]:
NullInjectorError: No provider for BaseURL! at NullInjector.get (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:11101:1) at R3Injector.get (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:11268:1) at R3Injector.get (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:11268:1) at NgModuleRef.get (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:25332:1) at Object.get (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:25046:1) at lookupTokenUsingModuleInjector (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:3342:1) at getOrCreateInjectable (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:3454:1) at ɵɵdirectiveInject (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:14737:1) at NodeInjectorFactory.MenuComponent_Factory [as factory] (ng:///MenuComponent/ɵfac.js:5:7) at getNodeInjectable (http://localhost:9876/karma_webpack/webpack:/node_modules/@angular/core/ivy_ngcc/fesm2015/core.js:3549:1)

Error: Expected undefined to be truthy. at at UserContext. (http://localhost:9876/karma_webpack/webpack:/src/app/menu/menu.component.spec.ts:46:23) at ZoneDelegate.invoke (http://localhost:9876/karma_webpack/webpack:/node_modules/zone.js/fesm2015/zone.js:372:1) at ProxyZoneSpec.onInvoke (http://localhost:9876/karma_webpack/webpack:/node_modules/zone.js/fesm2015/zone-testing.js:287:1)

spec.ts 的代码是：

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { MenuComponent } from './menu.component';
import { DishService } from '../services/dish.service';

describe('MenuComponent', () => {
  let component: MenuComponent;
  let fixture: ComponentFixture<MenuComponent>;

const mockDishService = {
  getDishes: () => {
     return {
        id: '000',
        name: 'nnnnn'
     }
  }
}

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      imports: [],
      declarations: [ MenuComponent ],
      providers: [
        { provide: DishService, useValue: mockDishService },
      ]
    })
    .compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(MenuComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();

  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });

});

组件代码为：

import { Component, OnInit, Inject } from '@angular/core';
import { Dish } from '../shared/dish';
import { DishService } from '../services/dish.service';
import { flyInOut, expand } from '../animations/app.animation';

@Component({
  selector: 'app-menu',
  templateUrl: './menu.component.html',
  styleUrls: ['./menu.component.scss'],
  // tslint:disable-next-line:use-host-property-decorator
  host: {
    '[@flyInOut]': 'true',
    'style': 'display: block;'
    },
  animations: [
    flyInOut(),
    expand()
  ]
})
export class MenuComponent implements OnInit {

  dishes!: Dish[];
  errMess: string;
  
  constructor(private dishService: DishService, 
    @Inject ('BaseURL') public baseURL) { }

  ngOnInit(): void {
    this.dishService.getDishes().subscribe((dishes => this.dishes = dishes), errMess => this.errMess = <any>errMess);
  }

}

我正在使用 baseURL 来获取 db.json 文件的信息，而运行 json-server --watch db.json 来模拟我得到来自服务器的信息，所以我有一个名为 baseurl.ts 的共享 .ts 文件，其中包含以下代码：

export const baseURL = 'http://localhost:3000';

并且在 app.module.ts 中我导入了 const

import { baseURL } from './shared/baseurl';

我将其添加为同一 app.module.ts 文件中的提供程序：

providers: [
    { provide: 'BaseURL', useValue: baseURL }
  ],

非常感谢有人帮助解决这个错误

Answer 1

问题 1：NullInjectorError

此错误消息显示为您的 DishComponent 需要 BaseURL 注入 [@Inject ('BaseURL')]。

NullInjectorError: R3InjectorError(DynamicTestModule)[BaseURL -> BaseURL]: NullInjectorError: No provider for BaseURL!

问题 1 的解决方案

确保在 providers 部分添加 BaseURL 进行单元测试。

const baseUrl = "your Base URL";

beforeEach(async () => {
  await TestBed.configureTestingModule({
    ...
    providers: [
      { provide: DishService, useValue: mockDishService },
      { provide: 'BaseURL', useValue: baseUrl },
    ]
  })
  .compileComponents();
});

问题 2：Return mockDishService.getDishes()

的错误值

来自MenuComponent，预计dishService.getDishes() return Observable<Menu[]> 或Observable<any[]> 类型的值。

dishes!: Dish[];

this.dishService.getDishes().subscribe((dishes => this.dishes = dishes), errMess => this.errMess = <any>errMess);

而mockDishService.getDishes() return是any或Menu类型的值，returned的数据是不匹配的。

const mockDishService = {
  getDishes: () => {
    return {
      id: '000',
      name: 'nnnnn',
    };
  },
};

因此您将收到如下错误消息：

TypeError: this.dishService.getDishes(...).subscribe is not a function

问题 2 的解决方案：

确保 mockDishService.getDishes() return 的 Observable<Menu[]> 或 Observable<any[]> 类型的值与真实的 dishService.getDishes().

匹配

import { of } from 'rxjs';

const mockDishService = {
  getDishes: () => {
    return of([
      {
        id: '000',
        name: 'nnnnn',
      },
    ]);
  },
};

Sample Solution on StackBlitz

测试时出现 NullInjectorError

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