Angular 6 Karma测试API问题

我不熟悉单元测试。我已经创建了一个Angular 6应用程序，希望进行单元测试。运行

ng测试后，我遇到一些错误


通知页面正在调用服务
NotificationService.getNotifications（）
，该服务在
notification.service.ts

通知组件测试文件：

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { HttpClientModule } from '@angular/common/http';
import { NotificationsPageComponent } from './notifications-page.component';
import { RouterTestingModule } from "@angular/router/testing";

import { AuthService } from '../../shared/auth/auth.service';

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

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      providers: [AuthService],
      declarations: [ NotificationsPageComponent ],
      imports: [HttpClientModule, RouterTestingModule]
    })
    .compileComponents();
  }));

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

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

此
api\u链接
来自
app config.service.ts

app config.service.ts

import { AppConfigService } from '../services/app-config.service';
import { AuthService } from '../shared/auth/auth.service';
....
export class NotificationService {
    ....
    getNotifications() {
        return this.http.get(this.appConfig.config.api_link + '/notes?show_on_dashboard=true', { headers: this.authService.header() })
        .pipe(map(res => JSON.stringify(res)));
    }
}

import { environment } from 'environments/environment';
export class AppConfigService {
    private appConfig;
    loadAppConfig() {
        this.http.get('./environments/env_settings.json').subscribe((data) => {
            this.appConfig = data;
            console.log('Environment variables loaded from env_settings.json');
            console.log(this.appConfig);
        },
        (err) => {
            console.warn("Error loading env_settings.json, using envrionment file instead");
            this.appConfig = environment;
        });
    }

    get config() {
        return this.appConfig;
    }
}

我在Karma控制台中遇到6个错误，所有错误都是相同的类型错误：无法读取未定义的属性“api_link”

任何帮助都将不胜感激

感谢您在测试规范中未提供AppConfigService