public void Given_TwoButterOneBread_WhenBuyTwoButterGetOneBreadHalfPrice_ReturnHalf()
        {
            var testData = new List <Product>
            {
                new Product
                {
                    PriceInPounds = 1.00m,
                    DisplayName   = "Bread",
                    Quantity      = 1,
                    Id            = Product.BreadId
                },
                new Product
                {
                    PriceInPounds = 0.80m,
                    DisplayName   = "Butter",
                    Quantity      = 2,
                    Id            = Product.ButterId
                }
            };

            var result = _offerService.BuyTwoButterGetOneBreadHalfPrice(testData);

            Assert.AreEqual(0.50m, result);
        }