What is it?
The Javascript Developer Plugin makes it easy to develop Javascript libraries, helpers, and even full applications in a Test-Driven or Behavior-Driven way. Building off of the excellent javascript_test plugin, this plugin includes generators for setting up javascript file and test skeletons as well as rake tasks to run the tests themselves.
This plugin makes use of jsUnit, as well as jsMock, a JavaScript mocking library.
Rubyforge project page is here.