每当我输入rails console进入终端（我在我的程序的根目录中），我就明白了：
/Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/values/time_zone.rb:270: warning: circular argument reference - now
/Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require': cannot load such file -- test/unit/testcase (LoadError)
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/test_case.rb:1:in `<top (required)>'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/console/app.rb:2:in `<top (required)>'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/application.rb:304:in `initialize_console'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/application.rb:152:in `load_console'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/commands/console.rb:27:in `start'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/commands/console.rb:8:in `start'
from /Users/TURNIPZ/.rvm/gems/ruby-2.2.1/gems/railties-3.2.13/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
如何摆脱这种情况并能够使用rails控制台？我认为这与https://teamtreehouse.com/forum/rails-console-not-fully-loading有关。我是一个完整的初学者，所以我可能需要一步一步的指导来解决问题。我该如何添加
gem 'test unit'
到我的gemfile。