    @Test
    void multipleDiscount() {

        assertThat(HarryPotter.getPrice(books(1, 1, 2, 2))).isEqualByComparingTo("30.40");
        assertThat(HarryPotter.getPrice(books(1, 1, 2, 3))).isEqualByComparingTo("29.60");
    }