Hiding /Shadowing of the methods

See more:

C#

.NET

class Program
    {
        static void Main(string[] args)
        {
            IInterface interfaceFromBase = new Base();

            Console.WriteLine(interfaceFromBase.test());

            Console.WriteLine(interfaceFromBase.test1());



            IInterface interfaceFromDerived = new Derived();

            Console.WriteLine(interfaceFromDerived.test());

            Console.WriteLine(interfaceFromDerived.test1());



            Console.ReadLine();
        }
    }

    interface IInterface
    {

        string test();

        string test1();

    }



    class Base : IInterface
    {

        public string test()
        {

            return "Test: I'm in Base";

        }



        public string test1()
        {

            return "Test1: I'm in Base";

        }

    }

    class Derived : Base ,IInterface
    {

        public new string test()
        {

            return "Test: I'm in Derived";

        }

    }

The output of the above function is
Test: I'm in Base
Test1: I'm in Base
Test: I'm in Derived
Test1: I'm in Base

If the Derived class is to be derived from Base only then the output would be
Test: I'm in Base
Test1: I'm in Base
Test: I'm in Base
Test1: I'm in Base

Would anyone please give me the difference?