public void initial_setup()
{
_shoppingCart = new MyShoppingCart.ShoppingCart();
_shoppingCart.AddPromotionsToCartItems(new PromotionOnProductA());
_shoppingCart.AddPromotionsToCartItems(new PromotionOnProductB());
_shoppingCart.AddPromotionsToCartItems(new PromotionOnProductC());
_shoppingCart.AddPromotionsToCartItems(new PromotionOnProductD());
}