title: mocha expectation error when trying to bring up rails server
body: <p>I had a perfectly running rails project, but along the lines i had to reinstall a couple of gems and switched between rbenv and rvm. I was previously running rvm, then i switched to rbenv, started getting a bunch of exceptions, tried switching back to rvm but still receiving the same errors.</p>
  
  <p>I'm inclined to believe this is not an rvm/rbenv issue, but rather a change in how my gems are getting installed.</p>
  
  <p>Here's the full stack trace:</p>
  
  <pre><code>&gt; rails s thin                                                                                                                                                                                                  kaush@Air-Kode
  DEPRECATION WARNING: Yajl's JSON gem compatibility API is going to be removed in 2.0
  ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/expectation_error.rb:5:in `&lt;module:Mocha&gt;': superclass mismatch for class ExpectationError (TypeError)
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/expectation_error.rb:3:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/expectation.rb:3:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/mock.rb:2:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/mockery.rb:2:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha/api.rb:2:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha_standalone.rb:1:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `block in load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:597:in `new_constants_in'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:225:in `load_dependency'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/activesupport-3.0.20/lib/active_support/dependencies.rb:242:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/mocha-0.10.0/lib/mocha.rb:2:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `each'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `block in require'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `each'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@global/gems/bundler-1.2.3/lib/bundler.rb:128:in `require'
      from ~/my_project/config/application.rb:7:in `&lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/railties-3.0.20/lib/rails/commands.rb:28:in `require'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/railties-3.0.20/lib/rails/commands.rb:28:in `block in &lt;top (required)&gt;'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/railties-3.0.20/lib/rails/commands.rb:27:in `tap'
      from ~/.rvm/gems/ruby-1.9.2-p180@my-gemset/gems/railties-3.0.20/lib/rails/commands.rb:27:in `&lt;top (required)&gt;'
      from script/rails:6:in `require'
      from script/rails:6:in `&lt;main&gt;'
  </code></pre>
  
  <p>My gem versions:</p>
  
  <pre><code>   gem 'rails', '3.0.20'
     gem 'mocha'
  </code></pre>
  
  <p>This thing has been bugging me for the past 3 days, would appreciate any help...</p>