Running the complete test suite can be really long. You can running it on multi-fork system with the wonderfull gem of @tmm1, test-queue
If you want do it, you need install in first the gem 'test-queue'
gem install test-queue
After you just need launch the script with adapting runner of mongoid.
./script/rspec-queue-mongoid.rb spec
In my case, the complete test suite down to 2min after a 16min long before.