Ruby unit test doesn't do nothing

I'm really new to ruby. I'm starting to play following this guide for setting up ruby, rvm, update all my mac to current version, without any problem. So I installed test-unit gem and try some TDD script. Running the test nothing happen. So I run ruby with "-d" option and this happen.

Exception LoadError' at /Users/BlackSheep/.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems.rb:1222 - cannot load such file -- rubygems/defaults/operating_system ExceptionLoadError' at /Users/BlackSheep/.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems.rb:1231 - cannot load such file -- rubygems/defaults/ruby Exception LoadError' at /Users/BlackSheep/.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54 - cannot load such file -- test/unit ExceptionNoMethodError' at /Users/BlackSheep/.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:1984 - undefined method to_ary' for #<Gem::Specification:0x007fb10b1c5c78> ExceptionNoMethodError' at /Users/BlackSheep/.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:1984 - undefined method `to_ary' for #

what could be the problem?

ruby version 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]

rvm version 1.26.10

gem version 2.4.6