<p>How can I test <code>Controller.ViewData.ModelState</code>? I would prefer to do it without any mock framework.  </p>

You don't have to use a Mock if you're using the Repository Pattern for your data, of course.
Some examples:
http://www.singingeels.com/Articles/Test_Driven_Development_with_ASPNET_MVC.aspx
```
```
// Test for required "FirstName".
   controller.ViewData.ModelState.Clear();

   newCustomer = new Customer
   {
       FirstName = "",
       LastName = "Smith",
       Zip = "34275",    
   };

   controller.Create(newCustomer);

   // Make sure that our validation found the error!
   Assert.IsTrue(controller.ViewData.ModelState.Count == 1, 
                 "FirstName must be required.");
```
```