问题在ViewPage上调用扩展方法

using System.Web.Mvc;

namespace G3Site {
    public static class ViewPage_Extensions {
        public static void Test(this ViewPage vp) {
            vp.Writer.Write(\"this is a test\");
        }
    }
}

<%@ Import Namespace=\"G3Site\" %>

<% this.Test(); %>

<% Test(); %>

CS0103: The name \'Test\' does not exist in the current context

public class SomeClass
{
    public void Method()
    {
        ExtensionMethod();
    }
}

public static class Extensions
{
    public static void ExtensionMethod(this SomeClass sc) { }
}