http://johnbintz.github.com/jasmine-headless-webkit/
install:
gem install guard-jasmine-headless-webkit
add the necessary bits to your Guardfile to test a Rails 3.1:
guard init jasmine-headless-webkit
run:
bundle exec guard
bundle exec jasmine-headless-webkit -c
rake jasmine:headless
bundle exec jasmine-headless-webkit -c spec/javascripts/api_spec.coffee