How to unit test MVC Controller Action that calls a service associated with the Controller

Ok, i tried. but i can't wrap my head around this.

I have a Controller

public sealed class CourseController : ExtController
{
 [HttpPost, PersistState, InRole("")] //TODO [SECURITY] [FIX] UPDATE SECURITY ROLES ]

    public ActionResult Create(string[] flags, string name, string code, string description)
    {
        try
        {
            var Course = Svc.ProcessOperation("CreateCourse", new
            {

                Flags = flags.Merge(",")
            });



            Svc.ProcessOperation("CreateCourseTranslation", new
            {
                CourseId = Course.EntityID,
                LanguageId = JAs.Int32(Svc.Localization.Language.EntityID),
                Name = name,
                Description = description,
                Code = code

            });
            TempData.PersistStatus("Success");

            return View();
        }
        catch (Exception ex)
        {
            ModelState.AddModelError("API", ex);
            TempData.PersistStatus("Failed");
        }
        return RedirectToAction("Create");
    }
}

Svc is a public property of type Service inside the ExtController abstract class which in turn extends the Controller Class

 /// <summary>
/// Represents the exteded controller.
/// </summary>
public abstract class ExtController : Controller
{
    #region Properties

    /// <summary>
    /// Gets the service associated with the controller.
    /// </summary>
    public Service Svc
    {
        get
        {
            return HttpContext.Svc();
        }
    }

    #endregion
}

and here is the Unit Test Code using NUnit

 [Test]
    public void Create_HttpPost_Action_Returns_Create_View()
    {
        // Arrange          
        var customersController = new CourseController();

        // Act
        var result = customersController.Create(new[] { "None" }, "courseName", "Code", "description") as ViewResult;

        // Assert
        Assert.IsNotNull(result, "Should have returned a ViewResult");
        result.AssertViewRendered().ForView("Create");

    }

The Problem is when the Create method is called it needs to use Svc to process the operation, so i guess i have to Mock that! but i can't figure out how.

should i mock the controller! but i can't because its a sealed class! or the ExtController! I am lost and need guidance.

[FWIW] This project is based on Xenta MVC Framework (Open Source) which has this Architecture Overview