title: import file mismatch in pytest
body: <p>I've got a file in the package with 'test' in its name and when I run pytest I got an error </p>
  
  <pre><code>import file mismatch:
  imported module 'my_project.my_file_test' has this __file__ attribute:
    /my_project/src/my_project/build/lib/python2.7/site-packages/foo/my_file_test.py
  which is not the same as the test file we want to collect:
    /my_project/src/my_project/build/private/python2.7/lib/foo/my_file_test.py
  HINT: remove __pycache__ / .pyc files and/or use a unique basename for your test file modules
  </code></pre>
  
  <p>If I remove 'test' from the file it works fine but unfortunately I can't change it.</p>
  
  <p>So the question is how to tell pytest to ignore this file?</p>