Angular testing spyOn on private variable

Question

How test the call on method of private variable ? I must test the call of unsubscribe method when the ngOnDestroy is called.

There is my code

import { Component, OnInit } from '@angular/core';
import { Subscription } from 'rxjs/Subscription';
import { LoaderService } from '@core/components/loaders/services/loader.service';

@Component({
  selector: 'loader-mask',
  templateUrl: './loader-mask.component.html',
  styleUrls: ['./loader-mask.component.css']
})

export class LoaderMaskComponent implements OnInit {

  show = false;
  private subscription: Subscription;

  constructor(private loaderService: LoaderService) { }

  ngOnInit() {
    this.subscription = this.loaderService.loaderState
      .subscribe((state: boolean) => {        
        this.show = state;
      });
  }

  ngOnDestroy() {    
    if (this.subscription)
      this.subscription.unsubscribe();
    }
}

There is my test code

it('should destroy the subscription when destroying', () => {
    const spyUnSubscribe = spyOn(component['subscription'], 'unsubscribe').and.callThrough();
    component.ngOnDestroy();  
    expect(spyUnSubscribe).toHaveBeenCalled();  
    expect(component['subscription']).toBeUndefined();
  });

There is the issue :

Error: <spyOn> : could not find an object to spy upon for unsubscribe()
Usage: spyOn(<object>, <methodName>)

Caucus

You are subscribing to the service so you could mock/spy the service and control the returned observable and spy on it. – Rider

you cannot access private properties at all. that is why they are private – Ophthalmia

any answer on it? – Vasoinhibitor

Answer 1

Put any before spyOn to cheat Typescript compilator.

spyOn<any>(component['subscription'], 'unsubscribe')

Ailsa

Answer 2

Actually something similar like this worked for me

spyOn(loginComponent['loaderSubscription'], 'unsubscribe');
loginComponent.ngOnDestroy();
expect(loginComponent['loaderSubscription'].unsubscribe).toHaveBeenCalled();

Vasoinhibitor