This is definitely what we want to do next, but I've got quite a few comments on how we want to do this:

• I'd like it to be under the jt test command, so it should be jt test mri.
• I'd like it to be able to specify a directory or a single file, so I can do jt test mri test/mri/ruby/test_whileuntil.rb or jt test mri test/mri/ruby/test_whileuntil.rb
• You're re-using JRuby's excludes there, which doesn't make any sense - can you create a full set of excludes for Truffle under test/truffle/excludes (may need to talk to @headius about how to do that)
• You might want to modify jt tag, jt untag, and jt tag all to work with these excludes if they see a MRI test path rather than a RubySpec path
• Do these tests actually work for us? Last time I checked we didn't run test/unit very well - if we do now that's excellent news
• When it works and we have everything that doesn't pass excluded, we should add it to Travis

This patch would still be useful with just the first two points addressed.

@chrisseaton The first two points work now, jt test mri and jt test mri test/mri/ruby/test_whileuntil.rb
(I tested the command without -X+T).

I've ran a little bit of test/unit successfully. The first failure we'll run into here is:

/Users/brandonfish/Documents/jruby-mine/test/mri/lib/minitest/unit.rb:1389:in `(singleton-def)': undefined method `method_added' for #<Class:0x114> (NoMethodError)
    from /Users/brandonfish/Documents/jruby-mine/test/mri/lib/minitest/unit.rb:1388:in `TestCase'
    from /Users/brandonfish/Documents/jruby-mine/test/mri/lib/minitest/unit.rb:1242:in `Unit'
    from /Users/brandonfish/Documents/jruby-mine/test/mri/lib/minitest/unit.rb:746:in `MiniTest'
    from /Users/brandonfish/Documents/jruby-mine/test/mri/lib/minitest/unit.rb:12:in `<main>'
    from /Users/brandonfish/Documents/jruby-mine/test/mri/lib/test/unit.rb:5:in `<main>'
    from test/mri/runner.rb:7:in `<main>'

Great - I'll merge after pre2 is out.