Can't run rake test in Rubymine with Ruby 1.9

This one has happened several times to me on new installs but I figured I should finally write something up about it. If you're using Rubymine (which I would highly recommend) with Ruby 1.9, and you attempt to run rake test using the built in rake task tools in Rubymine, you'll get an error that says "File 'test/unit/autorunner.rb' not found in $LOAD_PATH of Ruby SDK ...". There is an easy fix for this. Just install and attach the test-unit gem.