Simple singleton pattern

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace singleton
{
    class Program
    {
        static void Main(string[] args)
        {
            Singleton s1 = Singleton.GetInstance();
            Singleton s2 = Singleton.GetInstance();
            Console.WriteLine(s2.ToString());
            Console.WriteLine(s1.ToString());
            Console.ReadLine();
        }
    }

    // NOT THREADSAFE and it is LAZY
    class Singleton
    {
        static Singleton instance;

        // single, STATIC entry point
        public static Singleton GetInstance()
        {
            if (instance == null)
                instance = new Singleton();
            return instance;
        }

        int _test;
        public int test
        {
            get { return _test; }
            set { _test = value; }
        }

        private Singleton()
        {
            test = new Random().Next(1000);
        }

        public override string ToString()
        {
            return test.ToString();
        }
    }
}