If you want a thing done well ....

...and continuously, and consistent way, let the computer do it for you.

gem install ZenTest
gem install autotest-rails
gem install redgreen

If you're on MAC:

gem install autotest-fsevent
echo "require 'autotest/fsevent'\nrequire 'redgreen'" >> ~/.autotest

If you're on GNU/Linux

gem install autotest-inotify
echo "require 'autotest/inotiny'\nrequire 'redgreen'" >> ~/.autotest


just run 'autotest' from your project root directory, and it will run the relevant tests on your modified files.