public void EmptySkusTest()
        {
            //Arrange
            IList <OrderLine> orderLines = PromotionEngine.GetOrderLines("D");
            PromotionEngine   engine     = new PromotionEngine(orderLines);

            //Act
            decimal actualTotal = engine.Calculate();

            //Assert
            decimal expectedTotal = 0;

            Assert.AreEqual(expectedTotal, actualTotal);
        }