使用角度2添加firebase的单元测试

有没有人知道如何使用角度2来测试基本的firebase添加项目进行基本单元测试.

我的代码使用的是typescript而不是基本的JavaScript

这就是我正在测试的:

 export class AppComponent {
     ref: Firebase;
     refUsers: Firebase;
     refProfiles: Firebase;

     constructor(){
         this.ref = new Firebase("https://markng2.firebaseio.com");
         this.refUsers = new Firebase("https://markng2.firebaseio.com/users");
         this.refProfiles = new Firebase("https://markng2.firebaseio.com/profiles");    
     }

     public addUser(newUser: Object): void{     
         this.refUsers.push(newUser, ()=>{

         });
     }
 }

这是我目前的测试:

 import {it, iit, describe, expect, inject, injectAsync, beforeEachProviders, fakeAsync, tick } from 'angular2/testing';
 import { AppComponent } from '../app/app';

 describe('AppComponent', () => {

     it('saves an item to Firebase', () => {
         let refUsers = new Firebase('');

         let service = new AppComponent();

         spyOn(service.refUsers, 'push');
         service.addUser({ item: true });

         expect(service.refUsers.push).toHaveBeenCalled();
     })

 });

这是我在运行测试时遇到的错误: