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

I've searched stackoverflow and googled four a couple of hours and still not found any solution for my "trivial" problem.

If you write unit test for your filtered [Authorize] ActionResult, how do you solve the problem to fake that user is authenticated?

I have a lot of ActionResult methods that are filtered with [Authorize] and I want to test all of my ActionResult methods regardless if they are filtered with [Authorize] or not.

A simple example of what i mean:

[TestMethod]
public void Create_Get_ReturnsView()
{
 // Arrange
 var controller = new UserController();
 // Act
 var result = controller.Create();
 // Assert
 Assert.IsNotNull(result as ViewResult);
}

[Authorize]
public ActionResult Create()
{
 return View("Create");
}

As of now the tests don't even hit the ActionResult method because of the [Authorize] filter, exception thrown is: System.NullReferenceException: Object reference not set to an instance of an object.