NullInjectorError: StaticInjectorError(DynamicTestModule) 在 Angular 2 中测试时

Question

我是 Angular2 的新手，并试图在app.component.spec.ts文件中编写一个测试。我的应用程序相对简单，除了它从 3rd 方库（由同事编写）导入 LoginComponent 和 LogoutComponent 之外。这些组件现在分别用于路由登录或注销，非常简单。运行ng serve编译正常，应用程序“平稳”运行。ng test然而，Running给了我这个错误：

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

LogoutComponent 是从不同的项目导入的。此错误是否意味着我需要进入该项目并进行一些更改，还是应该在我的项目中以某种方式模拟 SessionService？

规格代码：

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TestBed像这样声明多个组件

 declarations: [AppComponent, TopNavComponent, LogoutComponent]

导致在测试调用时实例化多个组件compileComponents()。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，但该服务不存在于提供者中，因此您将获得NullInjectorError.

对此有两种解决方案：

• 只在declarations数组中声明一个组件并添加 schemas: [ CUSTOM_ELEMENTS_SCHEMA ]到TestBed配置对象中
• 继续声明多个组件并将每个组件的所有依赖项（或其模拟）添加到 providers数组中