Heroes: Testing addition of a hero

heroes.container.spec.ts

describe('adds a hero', () => {
  it('emits the specified hero when server responds', fakeAsync(() => {
    const wonderWoman = 'Wonder Woman';

    container.add(wonderWoman);
    tick();

    expect(observer).toHaveBeenCalledWith([
      ...femaleMarvelHeroes,
      { id: 42, name: wonderWoman },
    ]);
  }));
});