Heroes: Observing the heroes$ property of the container component

heroes.container.spec.ts

import { fakeAsync, tick } from '@angular/core/testing';
import { Subject } from 'rxjs';
import { takeUntil } from 'rxjs/operators';

import { HeroService } from '../hero.service';
import { HeroesContainerComponent } from './heroes.container';

describe(HeroesContainerComponent.name, () => {
  let container: HeroesContainerComponent;
  const destroy: Subject<void> = new Subject();
  const heroServiceStub: jasmine.SpyObj<HeroService> = createHeroServiceStub();
  const observer: jasmine.Spy = jasmine.createSpy('heroes observer');

  beforeEach(fakeAsync(() => {
    container = new HeroesContainerComponent(heroServiceStub);
    container.heroes$.pipe(takeUntil(destroy)).subscribe(observer);
    tick();
  }));

  afterEach(() => {
    destroy.next();
    observer.calls.reset();
    resetHeroServiceStub(heroServiceStub);
  });

  afterAll(() => {
    destroy.complete();
  });
});