RCov is used to find out what percentage of your codebase is being covered by your tests, and RCov is discussed in chapter 25 of our book, Practical Rails Plugins.
Installation:
gem install rcov ruby ./script/plugin install http://svn.codahale.com/rails_rcov
Example:
rake test:units:rcov
For more information, check out the following sites: Rcov Homepage Rails RCov Homepage
Author: Gem by Mauricio Fernandez, Plugin by Coda Hale