How to mock AngularFire 2 service in unit test?

I'm trying to set up unit tests for a sample Angular 2 app using AngularFire 2 auth, the component is fairly simple:

import { Component } from '@angular/core';
import { AngularFire, AuthProviders } from 'angularfire2';

@Component({
  moduleId: module.id,
  selector: 'app-root',
  templateUrl: 'app.component.html',
  styleUrls: ['app.component.css']
})
export class AppComponent {
  isLoggedIn: boolean;

  constructor(public af: AngularFire) {
    this.af.auth.subscribe(auth => {
      if (auth) {
        this.isLoggedIn = true;
      } else {
        this.isLoggedIn = false;
      }
    });
  }

  loginWithFacebook() {
    this.af.auth.login({
      provider: AuthProviders.Facebook
    });
  }

  logout() {
    this.af.auth.logout();
  }
}

All I'm doing is wrapping around the login and logout methods in AngularFire so I was thinking about using a mock to check if the methods were called but I'm not sure where to start, I tried doing the following in my spec file:

import { provide } from '@angular/core';
import { AngularFire } from 'angularfire2';
import {
  beforeEach, beforeEachProviders,
  describe, xdescribe,
  expect, it, xit,
  async, inject
} from '@angular/core/testing';
import { AppComponent } from './app.component';

spyOn(AngularFire, 'auth');

beforeEachProviders(() => [
  AppComponent,
  AngularFire
]);

describe('App Component', () => {
  it('should create the app',
    inject([AppComponent], (app: AppComponent) => {
      expect(app).toBeTruthy();
    })
  );

  it('should log user in',
    inject([AppComponent], (app: AppComponent) => {
      expect(app.fb.auth.login).toHaveBeenCalled();
    })
  );

  it('should log user out',
    inject([AppComponent], (app: AppComponent) => {
      expect(app.fb.auth.logout).toHaveBeenCalled();
    })
  );
});

However I'm not sure how to mock the login and logout methods since they're part of the auth property, is there a way to mock auth and also the returning login and logout methods?