title: pytest cannot import module while python can
body: <p>I am working on a package in Python. I use virtualenv. I set the path to the root of the module in a .pth path in my virtualenv, so that I can import modules of the package while developing the code and do testing (Question 1: is it a good way to do?). This works fine  (here is an example, this is the behavior I want):</p>
  
  <pre><code>(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ python
  Python 2.7.12 (default, Jul  1 2016, 15:12:24) 
  [GCC 5.4.0 20160609] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; from rc import ns
  &gt;&gt;&gt; exit()
  (VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ python tests/test_ns.py 
  issued command: echo hello
  command output: hello
  </code></pre>
  
  <p>However, if I try to use PyTest, I get some import error messages:</p>
  
  <pre><code>(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ pytest
  =========================================== test session starts ============================================
  platform linux2 -- Python 2.7.12, pytest-3.0.5, py-1.4.31, pluggy-0.4.0
  rootdir: /home/zz/Desktop/GitFolders/rc, inifile: 
  collected 0 items / 1 errors 
  
  ================================================== ERRORS ==================================================
  ________________________________ ERROR collecting tests/test_ns.py ________________________________
  ImportError while importing test module '/home/zz/Desktop/GitFolders/rc/tests/test_ns.py'.
  Hint: make sure your test modules/packages have valid Python names.
  Traceback:
  tests/test_ns.py:2: in &lt;module&gt;
      from rc import ns
  E   ImportError: cannot import name ns
  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  ========================================= 1 error in 0.09 seconds ==========================================
  (VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ which pytest
  /home/zz/Desktop/VirtualEnvs/VEnvTestRc/bin/pytest
  </code></pre>
  
  <p>I am a bit puzzled, it looks like this indicates an import error, but Python does it fine so why is there a problem specifically with PyTest? Any suggestion to the reason / remedy (Question 2)? I googled and stack-overflowed the 'ImportError: cannot import' error for PyTest, but the hits I got were related to missing python path and remedy to this, which does not seem to be the problem here. Any suggestions?</p>