Test for failure to subscribe to an Observable with Jasmine

Question

In my Angular2 app which uses AngularFire2, I have an AuthService which tries to authenticate anonymously with Firebase.

I am trying to write a test that expects the subscription to the AngularFireAuth's authState to fail (an exceptional termination of the observable sequence) and an error to be thrown.

I have asked a what appears to be a similar question, however, here I am testing for an "exceptional termination of the observable sequence" — a catastrophic failure e.g. when the 3rd party provider Firebase is down.

This is separate to my other (related) question where I am testing for a rejected promise.

Here is a simplified AuthService:

import { Injectable } from '@angular/core';

import { AngularFireAuth } from 'angularfire2/auth';
import * as firebase from 'firebase/app';
import { Observable } from 'rxjs/Rx';

@Injectable()
export class AuthService {
  private authState: firebase.User;

  constructor(private afAuth: AngularFireAuth) { this.init(); }

  private init (): void {
    this.afAuth.authState.subscribe((authState: firebase.User) => {
      if (authState === null) {
        this.afAuth.auth.signInAnonymously()
          .then((authState) => {
            this.authState = authState;
          })
          .catch((error) => {
            throw new Error(error.message);
          });
      } else {
        this.authState = authState;
      }
    }, (error) => {
      throw new Error(error.message);
    });
  }
}

And here are my test specs:

import { TestBed, inject } from '@angular/core/testing';

import { AngularFireAuth } from 'angularfire2/auth';
import 'rxjs/add/observable/of';
import { Observable } from 'rxjs/Rx';

import { AuthService } from './auth.service';
import { environment } from '../environments/environment';

describe('AuthService', () => {
  const mockAngularFireAuth: any = {
    auth: jasmine.createSpyObj('auth', {
      'signInAnonymously': Promise.resolve('foo'),
      // 'signInWithPopup': Promise.reject(),
      // 'signOut': Promise.reject()
    }),
    authState: Observable.of(null)
  };

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        { provide: AngularFireAuth, useValue: mockAngularFireAuth },
        { provide: AuthService, useClass: AuthService }
      ]
    });
  });

  it('should be created', inject([ AuthService ], (service: AuthService) => {
    expect(service).toBeTruthy();
  }));

  //
  //
  //
  //
  //

  describe('when we can’t authenticate', () => {
    beforeEach(() => {
      mockAngularFireAuth.auth.signInAnonymously.and.returnValue(Promise.reject('bar'));
    });

    it('should thow', inject([ AuthService ], (service: AuthService) => {
      expect(service).toThrow();
    }));
  });

  //
  //
  //
  //
  //

});

I'm not sure if this is even possible, or needed — as this would be a very exceptional case. If I'm going to start testing though I would like the tests to be as comprehensive and watertight as possible though! Thank you for your help!

Answer 1

I needed to spy on mockAngularFireAuth's authState and return an Observable that throws an error. When I subscribe to mockAngularFireAuth.authState in the onError function I should expect the error, a la:

import { TestBed, async, inject } from '@angular/core/testing';

import { AngularFireAuth } from 'angularfire2/auth';
import 'rxjs/add/observable/of';
import { Observable } from 'rxjs/Rx';

import { AuthService } from './auth.service';
import { MockUser} from './mock-user';
import { environment } from '../environments/environment';

describe('AuthService', () => {
  // An anonymous user
  const authState: MockUser = {
    displayName: null,
    isAnonymous: true,
    uid: '17WvU2Vj58SnTz8v7EqyYYb0WRc2'
  };

  const mockAngularFireAuth: any = {
    auth: jasmine.createSpyObj('auth', {
      'signInAnonymously': Promise.reject({
        code: 'auth/operation-not-allowed'
      }),
      // 'signInWithPopup': Promise.reject(),
      // 'signOut': Promise.reject()
    }),
    authState: Observable.of(authState)
  };

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        { provide: AngularFireAuth, useValue: mockAngularFireAuth },
        { provide: AuthService, useClass: AuthService }
      ]
    });
  });

  it('should be created', inject([ AuthService ], (service: AuthService) => {
    expect(service).toBeTruthy();
  }));

  …

  describe('catastrophically fails', () => {
    beforeEach(() => {
      const spy = spyOn(mockAngularFireAuth, 'authState');

      spy.and.returnValue(Observable.throw(new Error('Catastrophe')));
    });

    describe('AngularFireAuth.authState', () => {
      it('should invoke it’s onError function', () => {
        mockAngularFireAuth.authState.subscribe(null,
          (error: Error) => {
            expect(error).toEqual(new Error('Catastrophe'));
          });
      });
    });
  });
  …
});