public void GetCampaignDiscount_GiveCorrectDiscountAmount()
        {
            // jean:  50 x 10 = 500
            // apple: 2 x 50 = 100

            _shoppingCart.AddItem(jean, 10);
            _shoppingCart.AddItem(apple, 50);
            _shoppingCart.ApplyDiscounts(campaign1, campaign2, campaign3);
            _shoppingCart.GetTotalAmountAfterDiscounts();

            double campaignDiscount = _shoppingCart.GetCampaignDiscount();

            Assert.Equal(250, campaignDiscount);
        }
        public void AddProduct_Compaigndiscount()
        {
            var electronic = new Category("Electronic");
            var computer   = new Product("Lenovo Thinkpad X1", 1000, electronic);

            var campaign = new Campaign(electronic, 20, 2, DiscountType.Rate);

            shoppingCart.ApplyDiscounts(campaign);

            shoppingCart.AddItem(computer, 5);
            shoppingCart.AddItem(computer, 5);

            double totalAmount = shoppingCart.GetTotalAmountAfterDiscounts();

            Assert.AreEqual(8000, totalAmount);
        }