public void ShouldReduceInventory()
        {
            var supplier = new Supplier(null);
            var inventory = supplier.Inventory+supplier.UnfulfilledOrders;
            supplier.SetOrder(inventory);

            Assert.Equal(0,supplier.Inventory);
        }
        public void ShouldAddOverOrdersToUnFulfilled()
        {
            var supplier = new Supplier(null);
            var inventory = supplier.Inventory;
            var unfulfilledOrders = supplier.UnfulfilledOrders;
            supplier.SetOrder(inventory-unfulfilledOrders+5);

            Assert.Equal(5,supplier.UnfulfilledOrders);
        }