private static double CalculateDeliveryCost(ShoppingCart shoppingCart)
        {
            //TODO: Delivery costs should be dynamic
            var deliveryCostCalculator = new DeliveryCostCalculator
            {
                FixedCost       = 2.99,
                CostPerDelivery = 8,
                CostPerProduct  = 6
            };

            return(deliveryCostCalculator.CalculateDeliveryCost(shoppingCart));
        }