public void CalculateSpecialPriceThreeBItems_ShouldBe45()
        {
            var item         = _stock.StockList.Where(x => x.SKU == "B").SingleOrDefault();
            var specialPrice = new QuantitySpecialPrice(item, discountedPrice: 45, discountedQuantity: 2)
            {
            };

            var totalPrice = specialPrice.CalculateDiscountedPrice(item, 2);

            totalPrice.ShouldBe(45);
        }
        public void CalculateSpecialPriceThreeAItems_ShouldBe130()
        {
            var item         = _stock.StockList.Where(x => x.SKU == "A").SingleOrDefault();
            var specialPrice = new QuantitySpecialPrice(item, discountedPrice: 130, discountedQuantity: 3)
            {
            };

            var totalPrice = specialPrice.CalculateDiscountedPrice(item, 3);

            totalPrice.ShouldBe(130);
        }