def test_get_count_added(self):
        """
        Must return count how many users is reading some book.
        """
        third_book = Book.objects.get(book_name='Third Book')
        sixth_book = Book.objects.get(book_name='Sixth Book')
        not_existing_id = 10000

        self.assertEqual(AddedBook.get_count_added(third_book.id), 2)
        self.assertEqual(AddedBook.get_count_added(sixth_book.id), 4)
        self.assertEqual(AddedBook.get_count_added(not_existing_id), 0)

        removed_third = AddedBook.objects.filter(id_user=self.the_user1, id_book=third_book)
        removed_third.delete()

        removed_sixth = AddedBook.objects.filter(id_user=self.the_user1, id_book=sixth_book)
        removed_sixth.delete()

        self.assertEqual(AddedBook.get_count_added(third_book.id), 1)
        self.assertEqual(AddedBook.get_count_added(sixth_book.id), 3)
        self.assertEqual(AddedBook.get_count_added(not_existing_id), 0)