I created an extension method called HasContentPermission on the System.Security.Principal.IIdentity interface:

namespace System.Security.Principal
{
    public static bool HasContentPermission
        (this IIdentity itentity, int contentID)
    {
        // I do stuff here
        return result;
    }
}

And I call it like this:

bool hasPermission = User.Identity.HasPermission(contentID);

Works like a charm. Now I want to unit test it. To do that, all I really need to do is call the extension method directly, so:

using System.Security.Principal;

namespace MyUnitTests
{
    [TestMethod]
    public void HasContentPermission_PermissionRecordExists_ReturnsTrue()
    {
        IIdentity identity;
        bool result = identity.HasContentPermission(...

But HasContentPermission won't intellisense. I tried creating a stub class that inherits from IIdentity, but that didn't work either. Why?

Or am I going about this the wrong way?