I recently migrated an application to Rails 4 beta and all of my controllers specs broke up with this odd error.
After some investigation I noticed that ActionController::TestCase::Behavior.process method signature changed in Rails 4 while it seems RocketPants overrides this method in RocketPants::TestCase.
So, I made some changes to the RocketPants::TestCase.process method to make it compliant with the one in Rails 4 and now all my specs pass successfully.
You can find Rails 4 changes here : https://github.com/rails/rails/blob/master/actionpack/lib/action_controller/test_case.rb#L497
Well, unfortunately It doesn't work in Rails 3 but if this is something you're interested in, I have some ideas on how to make it backward compatible with Rails 3.
Looks like @keithpitt has fixed this in 53 - cheers!
Yep ! Still got an issue after, check my pull request :) !