Autotest on OSX

Download the required gems

# required for autotest and rails
sudo gem install autotest autotest-rails

# use osx 10.5 fsevent library instead of traversing the filesystem for changes (lowers CPU usage)
sudo gem install autotest-fsevent

# gives us pretty red, green messages upon failure and succes
sudo gem install redgreen

# provide growl notifications upon success and failures
sudo gem install autotest-growl

now we just include the gems we just installed in our ~/.autotest file

# require gems
require 'autotest/fsevent'
require 'autotest/growl'
require 'redgreen/autotest'

# tell autotest to ignore directories
Autotest.add_hook :initialize do |autotest|
%w{.git .svn .hg .DS_Store ._* vendor}.each {|exception| autotest.add_exception(exception) }
false
end