public void CanApplyStrawberriesSpecialOfferToStrawbsTrolley_ShouldReturn22_50()
        {
            // arrange
            var checkout = new Checkout(_strawbsTrolley);

            //act
            var discountedTrolley = checkout.ApplyStrawberriesSpecialOffer();
            var discountedTotal   = checkout.GetTotal();

            //assert
            Assert.AreNotEqual(discountedTrolley, null);
            Assert.AreEqual(discountedTrolley.Count(), 5);
            Assert.AreEqual(discountedTotal, 22.50);
        }