How to mock a observable stream while testing angular2 components?

Question

I am writing test cases for angular2 components.

I had created a service which uses observable stream as below:

import {Injectable}      from '@angular/core'
import {Subject} from 'rxjs/Subject';
import {User} from './user.model';

@Injectable()
export class UserService {

  selectedUserInstance:User = new User();

  // Observable selectedUser source
  private selectedUserSource = new Subject<User>();

  // Observable selectColumn stream
  selectedUser$ = this.selectedUserSource.asObservable();

  // service command
  selectUser(user:User) {
    this.selectedUserInstance=user;
    this.selectedUserSource.next(user);
  }
}

Now In my component I have subscribed to this stream as :

getSelectedUser() {
    this.subscriptionUser = this.userService.selectedUser$.subscribe(
      selectedUser => {
        this.selectedUser = selectedUser;
      }
    );
}

Now in my spec.ts file, I want to mock this stream as :

spyOn(userService, 'selectedUser$')
        .and.returnValue(Observable.of({
            'name': 'bhushan',
            'desc': 'student'
        }));

But it keeps giving me following error:

Error: spyOn could not find an object to spy upon for selectColumn$()

is there any way to do this?

I am stuck on this issue for very long time now.

any inputs?

thanks

Answer 1

selectedUser$ isn't a method, so you can't spy on it. Instead, if you want you can just assign it a your observable

rapidColumnService.selectedUser$ = Observable.of({
  'name': 'bhushan',
  'desc': 'student'
})

But honestly, if that is your complete service, I don't see why you even need to mock it. It is simple enough where using the real service probably wouldn't hurt. If you use the real service, then you can just selectUser whenever you want to emit something new to the component under test.

UPDATE

Another thing you could also do is instead of using an Observable is to use a Subject. A Subject is also an Observable, but it lets you emit values, making it easier to mock values to test.

rapidColumnService.selectedUser$ = new BehaviorSubject<any>();

Then when you want to send a value

rapidColumnService.selectedUser$.next({
  'name': 'bhushan',
  'desc': 'student'
});

Depending on how you have your component set up and the subscription, you may just want to use a plain Subject instead of a `BehaviorSubject. See this post for more info.