title: should pytest et al. go in tests_require[] or extras_require{testing[]}?
body: <p>I am writing a python program which uses py.test for testing and now one test also depends on numpy. Where in my setup.py should I add those dependencies?</p>
  
  <p>Currently the relevant part of my setup.py looks something like this:</p>
  
  <pre><code>[...]
  'version': '0.0.1',
  'install_requires': [],
  'tests_require': ['pytest'],
  'cmdclass': {'test': PyTest},
  'extras_require': {
      'testing': ['pytest'],
  },
  [...]
  </code></pre>
  
  <p>Having <code>pytest</code> twice feels already somewhat strange and I'm not sure where to add numpy.</p>