I just wanted to update ruby-core that JRuby is now running MRI's tests as part of our regular suite. We worked with Ryan Davis to design an extension to minitest called "excludes" which allows us to exclude certain class#method combinations from test runs. This has allowed us to start running MRI's tests and maintain a high-water mark of passing tests. minitest-excludes is available as a gem. I have a few pending fixes that should go into the next release that we needed to fully run MRI's suite, but it has been working very well so far. Currently we are just running test/ruby/** and most of the native extension tests. The others largely test stdlib that we share in common with MRI. After building JRuby, "rake test:mri19" will run the MRI 1.9.3 suite. JRuby's current excludes are here: https://github.com/jruby/jruby/tree/master/test/externals/ruby1.9/excludes We periodically sync 1.9.3's tests here: https://github.com/jruby/jruby/tree/master/test/externals/ruby1.9 And as always, we maintain any diffs of stdlib in our fork here: https://github.com/jruby/ruby/tree/jruby-ruby_1_9_3 We're very happy to be able to run MRI's tests along with our other suites. Hopefully over the coming months we'll be able to contribute improvements to the tests. Thank you! - Charlie