Program.cs

using System;

namespace SmallStore
{
    class Program
    {
        static void Main(string[] args)
        {

            //Create new Simple Store and InventoryRetailStore
            IStore galleryDePate = new SimpleStore();
            InventoryRetailStore invStore = new InventoryRetailStore();

            // Creation of Products 
            Product x1 = new Product(1, "Painting Picasso. Guernica", 100, 1000);
            Product x2 = new Product(2, "Painting Tsarouxis. Naftis A", 200, 2000);
            Product x3 = new Product(3, "Chair. Luis XV", 100, 1000);
            Product x4 = new Product(4, "Vase. Cubic", 500, 5000);
            
            //Samples transactions of SimpleStore
            galleryDePate.Buy(x1);
            galleryDePate.Buy(x3);
            galleryDePate.Sell(x1);
            Console.WriteLine(galleryDePate.GetRevenue());

            //Samples transactions of InvStore
            invStore.Buy(x1);
            invStore.Buy(x3);
            invStore.Sell(x1);
            Console.WriteLine(invStore.GetRevenue());
            invStore.Sell(x2);
            invStore.GetInventory();
            Console.WriteLine(invStore.GetRevenue());
        }
    }
}