public Money getSalePrice() {
    return price.minus(calculateDiscount());
  }
@Test
    void shouldGetSalePriceOfProduct() {
        assertEquals(Money.of(USD, 100), product.getSalePrice());

        product.setExpirationDate(LocalDate.now().plusDays(2));

        assertEquals(Money.of(USD, 80), product.getSalePrice());
    }