I tried converting the solution to .NET 4.0 - but it was too time consuming to do so. Instead I ripped out the pieces I needed, i.e. the route testing extension methods, and built a new assembly targeting the right versions of the framework. And I replaced RhinoMocks with Moq.
Using the Mvc.TestHelper assembly you can easily test routes with syntax like this:
"~/".ShouldMapTo<HomeController>(x => x.Index());
"~/Account/".ShouldMapTo<AccountController>(x => x.Register(null));
Note: I take zero credit for this work. All the source code is taken directly from the MVCContrib project.
I have made the source available on BitBucket so that you can test your MVC 3 routes. The project uses NUnit and Moq for testing.