gistfile1.cs

#pragma warning disable 0809
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public class Base
    {
        public virtual void Test1()
        {
        }
    }

    public class C : Base
    {
        [Obsolete]
        public override void Test1() // CS0809
        {
        }
    }

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

#pragma warning restore 0809