title: Conditional nosetests from bash
body: <p>I'm attempting to only run tests in files that have changed between git commits as part of our integration testing in Jenkins.</p>
  
  <p>The code below works, <em>unless</em> the filters remove all file results.  Then ALL tests get run by nose.  I would want no tests run in that case.</p>
  
  <pre><code>if [ $GIT_PREVIOUS_SUCCESSFUL_COMMIT != $GIT_COMMIT ]; then
      git diff --name-only --diff-filter=d $GIT_PREVIOUS_SUCCESSFUL_COMMIT $GIT_COMMIT | grep .py | xargs nosetests -vv
  fi
  </code></pre>
  
  <p>Any suggestions?</p>