title: How to show full Python Traceback with Tox/Py.test
body: <p>I'm using tox and py.test to run my Python unittests, and even though I'm using py.test's <code>--tb=long</code> option, errors are showing like:</p>
  
  <pre><code>E   ConftestImportFailure: (local('/myproject/tests/functional_tests/conftest.py'), (&lt;type 'exceptions.ImportError'&gt;, ImportError('No module named blah',), &lt;traceback object at 0x7fb5bb740518&gt;))
  </code></pre>
  
  <p>Tox is running the command:</p>
  
  <pre><code>py.test -rxs -rf -rs --ff --tb=long -x -k testname
  </code></pre>
  
  <p>How do I make is show the full traceback? I can't find anything mentioning this in the docs besides the <code>--tb</code> option.</p>