public void Buy_1_Book_Should_Pay_100()
        {
            // Arrange
            var shop = new Shop();

            // Act
            shop.AddOrders(new List<Book>{
                new Book{Id=1}
            });

            // Assert
            var actualTotal = shop.GetTotal();
            var expectedTotal = 100;
            Assert.AreEqual(expectedTotal, actualTotal);
        }
        public void Buy_2_Different_Books_Should_Pay_190()
        {
            // Arrange
            var shop = new Shop();

            // Act
            shop.AddOrders(new List<Book>{
                new Book{Id=1},
                new Book{Id=2},
            });

            // Assert
            var actualTotal = shop.GetTotal();
            var expectedTotal = 190;
            Assert.AreEqual(expectedTotal, actualTotal);
        }
        public void Buy_Book1_Book2_3Book3_Should_Pay_370()
        {
            // Arrange
            var shop = new Shop();

            // Act
            shop.AddOrders(new List<Book>{
                new Book{Id=1},
                new Book{Id=2},
                new Book{Id=3},
                new Book{Id=3},
            });

            // Assert
            var actualTotal = shop.GetTotal();
            var expectedTotal = 370;
            Assert.AreEqual(expectedTotal, actualTotal);
        }