When I upgraded to Rails 2.2 and a bunch of my controller tests started failing, I quickly realized that the rescue_from blocks were being skipped. I quick google turned up a solution that I quickly got working.

controller.use_rails_error_handling!

But since none of us wants to have to add this to each of our controller specs, add this to your configure block in spec_helper:

Spec::Runner.configure do |config|
  config.before(:each, :type=>:controller) {
    controller.use_rails_error_handling!}
end