auth.service.spec.ts

import { TestBed } from '@angular/core/testing';
import { AngularFireAuth } from '@angular/fire/auth';
import { AngularFirestore } from '@angular/fire/firestore';
import { BehaviorSubject } from 'rxjs';
import { AngularFireModule } from '@angular/fire';
import { AngularFireAuthModule } from '@angular/fire/auth';
import { AuthService } from './auth.service';

const FirestoreStub = {
  collection: (name: string) => ({
    doc: (_id: string) => ({
      valueChanges: () => new BehaviorSubject({ foo: 'bar' }),
      set: (_d: any) => new Promise((resolve, _reject) => resolve())
    })
  })
};

const FireAutStub = {
  collection: (name: string) => ({
    doc: (_id: string) => ({
      valueChanges: () => new BehaviorSubject({ foo: 'bar' }),
      set: (_d: any) => new Promise((resolve, _reject) => resolve())
    })
  })
};

describe('AuthService', () => {
  beforeEach(() =>
    TestBed.configureTestingModule({
      providers: [
        { provide: AngularFireAuth, useValue: FireAutStub },
        { provide: AngularFirestore, useValue: FirestoreStub }
      ],
      imports: [AngularFireModule, AngularFireAuthModule]
    })
  );

  it('AuthService should be created', () => {
    const service: AuthService = TestBed.get(AuthService);
    expect(service).toBeTruthy();
  });
});

auth.service.ts

import { Injectable } from '@angular/core';
import { AngularFireAuth } from '@angular/fire/auth';
import { AngularFirestore } from '@angular/fire/firestore';
import { Observable, of } from 'rxjs';
import { switchMap } from 'rxjs/operators';
import { User } from '@app/core/interfaces';

@Injectable({
  providedIn: 'root'
})
export class AuthService {
  user$: Observable<User>;

  constructor(private afAuth: AngularFireAuth, private afs: AngularFirestore) {
    this.user$ = this.afAuth.authState.pipe(
      switchMap(user => {
        if (user) {
          return this.afs.doc<User>(`user/${user.uid}`).valueChanges();
        } else {
          return of(null);
        }
      })
    );
  }
}