public void Can_parse_required_productvariant_ids()
        {
            var product = new Product
            {
                RequiredProductIds = "1, 4,7 ,a,"
            };

            var ids = product.ParseRequiredProductIds();
            ids.Length.ShouldEqual(3);
            ids[0].ShouldEqual(1);
            ids[1].ShouldEqual(4);
            ids[2].ShouldEqual(7);
        }
        /// <summary>
        /// Validates required products (products which require some other products to be added to the cart)
        /// </summary>
        /// <param name="customer">Customer</param>
        /// <param name="shoppingCartType">Shopping cart type</param>
        /// <param name="product">Product</param>
        /// <param name="storeId">Store identifier</param>
        /// <param name="automaticallyAddRequiredProductsIfEnabled">Automatically add required products if enabled</param>
        /// <returns>Warnings</returns>
        public virtual IList<string> GetRequiredProductWarnings(Customer customer,
            ShoppingCartType shoppingCartType, Product product,
            int storeId, bool automaticallyAddRequiredProductsIfEnabled)
        {
            if (customer == null)
                throw new ArgumentNullException("customer");

            if (product == null)
                throw new ArgumentNullException("product");

            var cart = customer.ShoppingCartItems
                .Where(sci => sci.ShoppingCartType == shoppingCartType)
                .LimitPerStore(storeId)
                .ToList();

            var warnings = new List<string>();

            if (product.RequireOtherProducts)
            {
                var requiredProducts = new List<Product>();
                foreach (var id in product.ParseRequiredProductIds())
                {
                    var rp = _productService.GetProductById(id);
                    if (rp != null)
                        requiredProducts.Add(rp);
                }
                
                foreach (var rp in requiredProducts)
                {
                    //ensure that product is in the cart
                    bool alreadyInTheCart = false;
                    foreach (var sci in cart)
                    {
                        if (sci.ProductId == rp.ID)
                        {
                            alreadyInTheCart = true;
                            break;
                        }
                    }
                    //not in the cart
                    if (!alreadyInTheCart)
                    {

                        if (product.AutomaticallyAddRequiredProducts)
                        {
                            //add to cart (if possible)
                            if (automaticallyAddRequiredProductsIfEnabled)
                            {
                                //pass 'false' for 'automaticallyAddRequiredProductsIfEnabled' to prevent circular references
                                var addToCartWarnings = AddToCart(customer: customer,
                                    product: rp, 
                                    shoppingCartType: shoppingCartType,
                                    storeId: storeId,
                                    automaticallyAddRequiredProductsIfEnabled: false);
                                if (addToCartWarnings.Count > 0)
                                {
                                    //a product wasn't atomatically added for some reasons

                                    //don't display specific errors from 'addToCartWarnings' variable
                                    //display only generic error
                                    warnings.Add(string.Format(_localizationService.GetResource("ShoppingCart.RequiredProductWarning"), rp.GetLocalized(x => x.Name)));
                                }
                            }
                            else
                            {
                                warnings.Add(string.Format(_localizationService.GetResource("ShoppingCart.RequiredProductWarning"), rp.GetLocalized(x => x.Name)));
                            }
                        }
                        else
                        {
                            warnings.Add(string.Format(_localizationService.GetResource("ShoppingCart.RequiredProductWarning"), rp.GetLocalized(x => x.Name)));
                        }
                    }
                }
            }

            return warnings;
        }