jruby-rcov

https://github.com/spicycode/rcov

rcov is a code coverage tool for Ruby. It is commonly used for viewing overall test unit coverage of target code. It features fast execution (20-300 times faster than previous tools), multiple analysis modes, XHTML and several kinds of text reports, easy automation with Rake via a RcovTask, fairly accurate coverage information through code linkage inference using simple heuristics, colorblind-friendliness...