Trouble with Rubinius and test-unit gem

test.rb

# Works fine with MRI and JRuby.

# Rubinius doesn't seem to pick up the gem, blows up with an error.
require 'rubygems'
gem 'test-unit'
require 'test/unit'

class TC_Foo < Test::Unit::TestCase
  test "test-unit 2 works as expected" do
    assert_true(1 == 1)
  end
end

# I definitely have the gem installed

>rbx -S gem list

*** LOCAL GEMS ***

rubygems-update (1.8.15)
test-unit (2.4.5)

# Here's my environment

>rbx -S gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.8.15
  - RUBY VERSION: 1.8.7 (yyyy-mm-dd patchlevel 0) [x86_64-apple-darwin10.8.0]
  - INSTALLATION DIRECTORY: /opt/test/rubinius/2.0/gems/1.8
  - RUBYGEMS PREFIX: /opt/test/rubinius/2.0
  - RUBY EXECUTABLE: /opt/test/rubinius/2.0/bin/rbx
  - EXECUTABLE DIRECTORY: /opt/test/rubinius/2.0/gems/1.8/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-10
    - x86_64-rubinius-2.0
  - GEM PATHS:
     - /opt/test/rubinius/2.0/gems/1.8
     - /Users/djberge/.gem/rbx/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

# Here's the error that indicates it's trying to use test-unit in the stdlib

>rbx test.rb
An exception occurred running test.rb
    method 'test': given 1, expected 3 (ArgumentError)

Backtrace:
    TC_Foo.__class_init__ (TC_Foo) at test.rb:6
                 Object#__script__ at test.rb:5
  Rubinius::CodeLoader#load_script at kernel/delta/codeloader.rb:67
  Rubinius::CodeLoader.load_script at kernel/delta/codeloader.rb:109
           Rubinius::Loader#script at kernel/loader.rb:630
             Rubinius::Loader#main at kernel/loader.rb:834
Loaded suite test
Started
F
Finished in 0.00357 seconds.

  1) Failure:
default_test(TC_Foo)
    [kernel/bootstrap/array.rb:68:in `each'
     kernel/bootstrap/array.rb:68:in `each']:
No tests were specified.

1 tests, 1 assertions, 1 failures, 0 errors

The output of $: after the "gem 'test-unit'" on line 5:

["/opt/test/rubinius/2.0/lib/18", "/opt/test/rubinius/2.0/gems/1.8/gems/test-unit-2.4.5/lib", "/opt/test/rubinius/2.0/site", "/opt/test/rubinius/2.0/site/x86_64-darwin10.8.0", "/opt/test/rubinius/2.0/vendor", "/opt/test/rubinius/2.0/vendor/x86_64-darwin10.8.0", "/opt/test/rubinius/2.0/lib", "."]

Here's the output of $: when using MRI:

["/usr/local/lib/ruby/gems/1.8/gems/test-unit-2.4.5/lib", "/usr/local/lib/ruby/site_ruby/1.8", "/usr/local/lib/ruby/site_ruby/1.8/i686-darwin10.8.0", "/usr/local/lib/ruby/site_ruby", "/usr/local/lib/ruby/vendor_ruby/1.8", "/usr/local/lib/ruby/vendor_ruby/1.8/i686-darwin10.8.0", "/usr/local/lib/ruby/vendor_ruby", "/usr/local/lib/ruby/1.8", "/usr/local/lib/ruby/1.8/i686-darwin10.8.0", "."]