It works well in simple cases. Running from Rake doesn’t work. Running rcov from rspec doesn’t work yet, either.
There are 13 unit tests that fail (12 failures and 1 error). The failures are mostly minor differences in output between MRI and JRuby. The big old up now is the one error. It appears to be a bug in the reset code. Once data collection starts, calling reset clears the callected data (desirable) and prevents new data from being collection (less desirable). I think that’s why running rcov from rspec fails.