test/unit now calls gem 'minitest', but this will create regressions for anyone using bundler.
For example, create an empty Gemfile and try bundle exec ruby -e "require 'test/unit'"
You get an error:
.rvm/gems/ruby-head@global/gems/bundler-1.5.3/lib/bundler/rubygems_integration.rb:240:in `block in replace_gem': minitest is not part of the bundle. Add it to Gemfile. (Gem::LoadError)
I think bundled test-unit should be rename like rbunit or ruby-unit. many of users is confused by bundled test-unit and test-unit gem.
If we can't merge their, it should be renamed.
I take the liberty to link to a branch with a beginning of patch that updates the bundled version of Minitest to 5 (https://github.com/robin850/ruby/compare/minitest-five) since this is more or less related to the problem here. IMO, this is really bad to have a "deprecated"/out dated version of a library that you're shipping with by default. I'm conscious that the amount of work would be pretty important to rename all Test::Unit::TestCase classes to Minitest::Test but the wrapper is not so nice.
Moreover, I don't think the amount of work needed to rename the test suite is really worth regarding the final result. The test cases would have to be renamed anyway if we follow Zachary's suggestion (which is legit, I think ; it would make no sense to have a ruby/unit.rb file with a Test::Unit class in it).
I find it sometimes annoying to have to create a Gemfile adding gem 'minitest' in it just to use an up to date version of Minitest.
I'm pretty sure you have good reasons to stuck with Test::Unit inside your test suite, but just my two cents here.