Test that Angular service have been initialized

Question

I am trying to test my Angular service using Karma-Jasmine and I need to be sure that after service is initialized loadApp function have been called. What is the best way to test it?

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

@Injectable()
export class GdlService {
  appName = 'myAppName';

  constructor(
    private ngZone: NgZone,
  ) {
    this.ngZone = ngZone;
    this.loadApp(this.appName);
  }


  private loadApp(appName) {
    this.ngZone.runOutsideAngular(() => {
      // ...some logic
    });
  }
}

Answer 1

It can be tested as any other function. Considering that loadApp is prototype method, it can be stubbed or spied on class prototype:

it('', () => {
  spyOn(<any>GdlService.prototype, 'loadApp');
  const gdl = TestBed.get(GdlService);
  expect(gdl['loadApp']).toHaveBeenCalledWith('myAppName');
});

Answer 2

Try mocking the injection for ngZone (I like ts-mockito for this sort of stuff) and then checking to see if ngZone.outsideOfAngular has been called. Due to the nature of typescript, I don't think you'll be able to directly spy on anything that is private comfortably.

Something like this in the test file:

import { GdlService } from 'place';
import { NgZone } from '@angular/core';
import { TestBed } from '@angular/core/testing';
import {
    anything,
    instance,
    mock,
    verify
} from 'ts-mockito';

describe('yada yada', () => {
    const mockNgZone = mock(NgZone);
    // Can use when(mockNgZone.whatever)... to mock what you need
    beforeEach(() => {
        TestBed.configureTestModule({
            providers: [{
                provide: NgZone,
                useValue: instance(mockNgZone)
            }]
        });
    });

    it('checks on loadApp', () => {
        verify(mockNgZone.runOutsideAngular(anything())).called();
    });
});

If you would prefer to just use the spyOn method instead, you can just replace the object in the useValue portion of the provider.