public void CanApplyTeaSpecialOfferToTwoOfEachItemShoppingTrolley_ShouldReturn35_57()
        {
            var checkout = new Checkout(_twoOfEachItemShoppingTrolley);

            var discountedTrolley = checkout.ApplyTeaSpecialOffer();
            var discountedTotal   = checkout.GetTotal();

            Assert.AreNotEqual(discountedTrolley, null);
            Assert.AreEqual(discountedTrolley.Count(), 6);
            Assert.AreEqual(discountedTotal, 35.57);
        }