Testing-ajax-example is a project mainly written in RUBY and JAVASCRIPT, it's free.
Example of testing autocomplete ajax without a browser
An Example of how to test AJAX (without the "J") calls using Cucumber and Webrat without a browser.
To try it out
To use in your project you'll need to copy features/step_definitions/autocomplete_steps.rb and features/support/autocomplete_steps_helper.rb.
I've written a description this technique at http://www.alexrothenberg.com/2009/05/testing-ajax-without-browser-with.html