I have been working my way through Scott Guthrie's excellent post on ASP.NET MVC Beta 1. In it he shows the improvements made to the UpdateModel method and how they improve unit testing. I have recreated a similar project however anytime I run a UnitTest that contains a call to UpdateModel I receive an ArgumentNullException naming the controllerContext parameter.

Here's the relevant bits, starting with my model:

public class Country {
  public Int32 ID { get; set; }
  public String Name { get; set; }
  public String Iso3166 { get; set; }
}

The controller action:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(Int32 id, FormCollection form)
{
  using ( ModelBindingDataContext db = new ModelBindingDataContext() ) {
    Country country = db.Countries.Where(c => c.CountryID == id).SingleOrDefault();

    try {
      UpdateModel(country, form);

      db.SubmitChanges();

      return RedirectToAction("Index");
    }
    catch {
      return View(country);
    }
  }
}

And finally my unit test that's failing:

[TestMethod]
public void Edit()
{
  CountryController controller = new CountryController();
  FormCollection form = new FormCollection();
  form.Add("Name", "Canada");
  form.Add("Iso3166", "CA");

  var result = controller.Edit(2 /*Canada*/, form) as RedirectToRouteResult;

  Assert.IsNotNull(result, "Expected to be redirected on successful POST.");
  Assert.AreEqual("Show", result.RouteName, "Expected to redirect to the View action.");
}

ArgumentNullException is thrown by the call to UpdateModel with the message "Value cannot be null. Parameter name: controllerContext". I'm assuming that somewhere the UpdateModel requires the System.Web.Mvc.ControllerContext which isn't present during execution of the test.

I'm also assuming that I'm doing something wrong somewhere and just need to pointed in the right direction.

Help Please!