Update: Phil Haack has updated his HttpContext Simulator with some new goodies.
Here is an article by Haacked showing how one can create a test friendly httpcontext.
I modified his example some and started using it in some tests; works very nice!
Here is another implementation based on Haack’s example that is supposed to also work with session.
I almost NEVER use session if I can avoid it, but still this could come in handy.