インタフェースの実装に関する動作について

interface ITest
{
    void Hoge();
}

class Test1 : ITest
{
    public void Hoge(){  Console.WriteLine("This is Test1."); }
}

class Test2 : Test1
{
    public new void Hoge(){  Console.WriteLine("This is Test2."); }
}

class Test3 : Test1, ITest
{
    public new void Hoge(){  Console.WriteLine("This is Test3."); }
}

static void Main(string[] args)
{
    ((ITest)new Test1()).Hoge();
    ((ITest)new Test2()).Hoge();
    ((ITest)new Test3()).Hoge();
}

This is Test1.
This is Test1.
This is Test3.