it('should call getBook', async() => {
    // given
    spyOn(booksService, 'getBook');

    // when
    const isbn = '9788306021486';
    component.ngOnInit();
    fixture.detectChanges();
    fixture.whenStable().then(() => {
        // then
        expect(booksService.getBook(isbn)).toHaveBeenCalled();
    });
});

it('should call addNewBook', async() => {
  // given
  spyOn(booksService, 'addNewBook');

  // when
  const book = new Book();
  component.ngOnInit();
  fixture.detectChanges();
  fixture.whenStable().then(() => {
      // then
      expect(booksService.addNewBook(book)).toHaveBeenCalled();
  });
});