Heroes: Testing addition of a hero

heroes.container.spec.ts

it('does not emit the specified hero when server fails', fakeAsync(() => {
  heroServiceStub.addHero.and.returnValue(
    throwError(new Error('server error'), asapScheduler));
  const scarletWitch = 'Scarlet Witch';

  container.add(scarletWitch);
  tick();

  expect(observer).not.toHaveBeenCalledWith([
    ...femaleMarvelHeroes,
    { id: 42, name: scarletWitch },
  ]);
}));