title: Prevent setup.py test / pytest from installing extra dependencies
body: <p>In my CI I have a <em>build</em> step, which uses <code>pip</code> and is correctly set up using private indexes etc. </p>
  
  <p>Then I have <em>test</em> step, which executes <code>python setup.py test</code>. 
  In this particular case <code>test</code> is an alias to <code>pytest</code>.</p>
  
  <p>Setuptools and PIP resolve package dependencies differently, which leads to <em>test</em> step attempting to re-install some of the packages. I would like to prevent that. Is there a way to do that either with Setuptools configuration (preferable) or with PyTest configuration?</p>
  
  <p><em>Update:</em></p>
  
  <p>By popular demand repos to exemplify the issue I'm having
  <a href="https://github.com/vartec/example_repo_setuptools_issue" rel="noreferrer">https://github.com/vartec/example_repo_setuptools_issue</a></p>