public void GetPrice_一二三集各買了一本_價格應為100_乘_3_乘_0點9_等於_270元()
        {
            //arrange
            var target = new ShoppingCart();
            var potterBook = new List<Book> {
                new Book { Name = "Potter第一集", Price = 100 },
                new Book { Name = "Potter第二集", Price = 100 },
                new Book { Name = "Potter第三集", Price = 100 }
            };
            var expected = 270;

            target.AddBookList(potterBook);

            //act
            var actual = target.GetPrice();

            //assert
            Assert.AreEqual(expected, actual);
        }