MVC Unit testing [Authorize(Roles="Role")]

So I have been googling this for a couple of hours and I am yet to find a working solution.

Here are a couple of questions I have found that paint the picture of what I've been doing but none give me a working answer.

How do I unit test a controller method that has the [Authorize] attribute applied?

Unit testing ASP.Net MVC Authorize attribute to verify redirect to login page

What I am trying to do is to write a unit that that checks the [Authorise(Roles="Role")] attribute on my controller actually allows/denies access to the controller based on the current user belonging/not belonging to a specific role.

The code below always returns the view even when I set IsInRole to false hence I figure it is ignoreing the Authorise attribute.

 [TestMethod]
    public void Auth_User_Can_Access()
    {
        //this test mocks a user and submits it as part of the context to the controller
        //Arrange
        Mock<IPrincipal> mockP = new Mock<IPrincipal>();
        mockP.SetupGet(p=>p.Identity.Name).Returns("UnitTesting");
        mockP.Setup(p=>p.IsInRole("Role")).Returns(false); //"Role" is not the actual role name.

        Mock<ControllerContext> mockC = new Mock<ControllerContext>();
        mockC.SetupGet(p=>p.HttpContext.User).Returns(mockP.Object);
        mockC.SetupGet(p=>p.HttpContext.Request.IsAuthenticated).Returns(true);

        AppsController target = new AppsController(mock.Object);
        target.ControllerContext = mockC.Object;

        // Act
        ViewResult result = target.Index() as ViewResult;

        // Assert
        Assert.IsNotNull(result);
    }

I'm clearly missing something here.

For completeness here is the start of my Controller code also

[Authorize(Roles = "Role")]

public class AppsController : Controller
{
     private IAppRepository db;

    public AppsController (IAppRepository appRepository)
    {
        db = appRepository;
    }

    // GET: Apps

    public ViewResult Index()
    {
        return View(db.Apps.ToList());
    }