title: pytest doesn't run any test
body: <p>pytest doesn't run any tests and it is not clear why. I tried to use --debug but didn't get any valuable information. It is completely not clear how to debug this sort of issues with pytest. (Looks like some issue with pytest configuration / env variables / test names patterns?)</p>
  <p>Example of test file:</p>
  <pre class="lang-py prettyprint-override"><code>import pytest
  
  
  @pytest.mark.sanity
  def test_me():
      &quot;&quot;&quot;I'm a test.&quot;&quot;&quot;
  
      assert True
  </code></pre>
  <p>But pytest doesn't run any test, why?</p>
  <pre><code>$ pytest
  ================================================== test session starts ===================================================
  platform linux2 -- Python 2.7.12, pytest-3.1.3, py-1.4.34, pluggy-0.4.0
  rootdir: /home/qawizard/pytest-hell, inifile:
  plugins: xdist-1.15.0, timeout-1.2.0
  collected 1 item s
  
  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Exit: Done! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  ============================================== no tests ran in 0.13 seconds ==============================================
  </code></pre>