javascript - 空注入(inject)器错误 : StaticInjectorError(DynamicTestModule) When Testing in Angular 2

Question

我是 Angular2 的新手，正在尝试在 app.component.spec.ts 文件中编写测试。我的应用程序相对简单，除了它从第 3 方库(由同事编写)导入 LoginComponent 和 LogoutComponent。这些组件现在分别用于路由登录或注销，非常简单的东西。运行 ng serve 编译正常，应用程序运行“顺利”。但是，运行 ng test 会出现此错误:

NullInjectorError: StaticInjectorError(DynamicTestModule)[LogoutComponent -> SessionService]: 
  StaticInjectorError(Platform: core)[LogoutComponent -> SessionService]: 
    NullInjectorError: No provider for SessionService!

LogoutComponent 是从另一个项目导入的。此错误是否意味着我需要进入该项目并进行一些更改，或者我是否应该以某种方式在我的项目中模拟 SessionService？

具体代码:

import {} from 'jasmine';
import {async, TestBed} from '@angular/core/testing';
import {RouterTestingModule} from '@angular/router/testing';
import {AuthErrorStateService, LogoutComponent} from '@custom-library';

import {AppComponent} from './app.component';
import {AppErrorStateService} from './core/error-states/app-error-state.service';
import {TopNavComponent} from './core/top-nav/top-nav.component';

describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed
        .configureTestingModule({
          imports: [RouterTestingModule],
          providers: [
            AppErrorStateService, AuthErrorStateService
          ],
          declarations: [AppComponent, TopNavComponent, LogoutComponent],
        })
        .compileComponents();
  }));

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

  it(`should have as title 'My App'`, () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.debugElement.componentInstance;
    expect(app.title).toEqual('My App');
  });

  it('should render title in a h1 tag', () => {
    const fixture = TestBed.createComponent(AppComponent);
    fixture.detectChanges();
    const compiled = fixture.debugElement.nativeElement;
    expect(compiled.querySelector('h1').textContent).toEqual('Welcome to My App!');
  });
});

Answer 1

问题是像这样在 TestBed 中声明多个组件

 declarations: [AppComponent, TopNavComponent, LogoutComponent]

导致在测试调用 compileComponents() 时实例化多个组件。发生这种情况时，declarations 数组中的每个组件都需要在 providers 数组中声明其依赖项才能完成实例化。声明的组件之一依赖于 SessionService，但提供者中不存在该服务，因此您会收到 NullInjectorError。

有两种解决方法:

• 在declarations数组中只声明一个组件并添加schemas: [ CUSTOM_ELEMENTS_SCHEMA ] 到 TestBed 配置对象
• 继续声明多个组件并添加所有每个组件的依赖项(或其模拟)providers 数组