public void PurchaseBook_ThreeBooks_CorrectTotalPrice()
        {
            ShoppingCart shoppingCart = new ShoppingCart();

            shoppingCart.AddBook1();
            shoppingCart.AddBook1();
            shoppingCart.AddBook1();

            Assert.IsTrue(shoppingCart.TotalPrice == 24);
        }
        public void PurchaseBook_TwoBookTypes_CorrectTotalPriceWithFivePercentDiscount()
        {
            ShoppingCart shoppingCart = new ShoppingCart();

            shoppingCart.AddBook1();
            shoppingCart.AddBook2();

            Assert.IsTrue(shoppingCart.TotalPrice == 15.2);
        }
        public void PurchaseBook_ThreeBookTypes_CorrectTotalPriceWithTenPercentDiscount()
        {
            ShoppingCart shoppingCart = new ShoppingCart();

            shoppingCart.AddBook1();
            shoppingCart.AddBook2();
            shoppingCart.AddBook3();

            Assert.IsTrue(shoppingCart.TotalPrice == 21.6);
        }
        public void PurchaseBook_FourDifferentBooks_CorrectTotalPriceWithTwentyPercentDiscount()
        {
            ShoppingCart shoppingCart = new ShoppingCart();

            shoppingCart.AddBook1();
            shoppingCart.AddBook2();
            shoppingCart.AddBook3();
            shoppingCart.AddBook4();

            Assert.IsTrue(shoppingCart.TotalPrice == 25.6);
        }