title: Stubbing Paperclip S3 requests in specs
body: <p>I am using Paperclip and S3 for image uploads and am trying to stub out calls to S3 from my test suite.  I found the thoughtbot post which mentions doing </p>
  
  <pre><code>  a.cover       { a.paperclip_fixture('album', 'cover', 'png') }
  </code></pre>
  
  <p>but that gives me a "wrong number of arguments (4 for 2)" error.  I tried switching the arguments above to an array, which removes the original error, but gives an error saying "Attribute already defined: paperclip_fixture".</p>
  
  <p>Has anyone been able to get this working?  Also, I'd ideally like to use the local filesystem for the development environment.  Is there an easy way to do this?</p>