def test_prepare_new_book(self):
empty_book = models.Book()
result = command.prepare_book(empty_book, 'now')
assert isinstance(result, models.Book)
assert result.created_at == 'now'
def test_prepare_old_book(self):
dated_book = models.Book(created_at='last week')
result = command.prepare_book(dated_book, 'now')
assert isinstance(result, models.Book)
assert result.created_at == 'last week'