Solution : gem install minitest /usr/lib/ruby/gems/1.9.1/gems/turn-0.9.4/lib/turn/minitest.rb:23:in `': MiniTest v1.6.0 is out of date. (RuntimeError) `gem install minitest` and add `gem 'minitest' to you test helper.

My system info was like:
OS: Ubuntu 11.10
Ruby: version 1.9.2p290
Rails: version 3.1.1
Minitest gem: 2.12.1
I've had the following error when I tried to run the test command for my rails application.

rake test

The error message was like this: (Click on the image to read the text)

change the gemfile of the project and add the following lines:


group :test do

  gem "minitest"
end

Had a quite good test experience. 
Happy coding.