Using the Beta 1 of ASP.NET MVC I was trying to use Moq to test a controller action that used the UpdateModel using a FormCollection as the value provider. Reading Scott Guthrie's post for Beta 1 he makes it clear that it should be possible not to mock the context for the controller to descrease unit test friction - however any use of the UpdateModel generates an ArgumentNullException...
So I still had to mock - hopefully this will be worked out in the next beta but for now using Moq this is the minimum required to Mock the ControllerContext.
var routeData = new RouteData();
var httpContext = new Mock<HttpContextBase>();
var controllerContext = new Mock<ControllerContext>(httpContext.Object, routeData,controller);
controller.ControllerContext = controllerContext.Object;