title: Rspec extremely slow, one file needs 4 second to execute
body: <p>I'm using <code>spring (1.1.3)</code>  and <code>Rails 4.1.6</code></p>
  
  <p>But as you can see, the execute time is really slow ?</p>
  
  <p>How to profile the bottleneck ? Thanks</p>
  
  <pre><code>% bundle exec bin/rspec spec/models/tool/cvt/streaming_verification_spec.rb
  .rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/actionpack-4.1.6/lib/action_dispatch/http/mime_type.rb:163: warning: already initialized constant Mime::PDF
  .rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/actionpack-4.1.6/lib/action_dispatch/http/mime_type.rb:163: warning: previous definition of PDF was here
  "show combination"
  .
  
  Finished in 0.00119 seconds (files took 4.42 seconds to load)
  1 example, 0 failures
  </code></pre>
  
  <h2>Gem about rspec</h2>
  
  <pre><code>  * guard-rspec (4.3.1)
    * rspec (3.1.0)
    * rspec-core (3.1.5)
    * rspec-expectations (3.1.2)
    * rspec-mocks (3.1.2)
    * rspec-rails (3.1.0)
    * rspec-support (3.1.1)
  </code></pre>