title: Change pytest rootdir
body: <p>I am stuck with this incredibly silly error. I am trying to run pytest on a Raspberry Pi using bluepy. </p>
  
  <pre><code>pi@pi:~/bluepy/bluepy $ pytest test_asdf.py
  ============================= test session starts       ==============================
  platform linux2 -- Python 2.7.9, pytest-3.0.7, py-1.4.33, pluggy-0.4.0
  rootdir: /home/pi/bluepy, inifile:
  collected 0 items / 1 errors
  
  ==================================== ERRORS ====================================
   ______________ ERROR collecting bluepy/test_bluetoothutility.py _______________
  ImportError while importing test module '/home/pi/bluepy/bluepy/test_asdf.py'.
  Hint: make sure your test modules/packages have valid Python names.
  Traceback:
  test_asdf:4: in &lt;module&gt;
      from asdf import AsDf
  asdf.py:2: in &lt;module&gt;
      from bluepy.btle import *
  E       ImportError: No module named btle
  !!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
  =========================== 1 error in 0.65 seconds ============================
  </code></pre>
  
  <p>I realised that my problem could be that rootdir is showing incorrect path. It should be </p>
  
  <pre><code>/home/pi/bluepy/bluepy
  </code></pre>
  
  <p>I've been reading <a href="http://doc.pytest.org/en/latest/customize.html" rel="noreferrer" title="pytest docs">pytest docs</a> but I just do not get it how to change the rootdir. </p>