I am trying to write a unit test for my one controller to verify if a view was returned properly, but this controller has a basecontroller that accesses the HttpContext.Current.Session. Everytime I create a new instance of my controller is calls the basecontroller constructor and the test fails with a null pointer exception on the HttpContext.Current.Session. Here is the code:

public class BaseController : Controller
{       
    protected BaseController()
    {
       ViewData["UserID"] = HttpContext.Current.Session["UserID"];   
    }
}

public class IndexController : BaseController
{
    public ActionResult Index()
    {
        return View("Index.aspx");
    }
}

    [TestMethod]
    public void Retrieve_IndexTest()
    {
        // Arrange
        const string expectedViewName = "Index";

        IndexController controller = new IndexController();

        // Act
        var result = controller.Index() as ViewResult;

        // Assert
        Assert.IsNotNull(result, "Should have returned a ViewResult");
        Assert.AreEqual(expectedViewName, result.ViewName, "View name should have been {0}", expectedViewName);
    }

Any ideas on how to mock the Session that is accessed in the base controller so the test in the descendant controller will run?