public void Then_the_product_should_be_removed()
        {
            var newQty = new NonNegativeQuantity(0);

            _basket.ChangeQuantityOfProduct(newQty, _product);

            Assert.IsNull(_basket.Items().FirstOrDefault(i => i.Product == _product));
        }
        public void Then_the_quantity_of_that_product_should_update_to_match()
        {
            var newQty = new NonNegativeQuantity(5);

            _basket.ChangeQuantityOfProduct(newQty, _product);

            Assert.AreEqual(newQty.Value, _basket.Items().FirstOrDefault(i => i.Product == _product).Quantity.Value);
        }