How to configure properly unit testing with Errbot?

I tried to follow this guide http://errbot.io/en/latest/user_guide/plugin_development/testing.html

I installed pytest and launch it with

pytest --rootdir='./srv/plugins'

but I have this following error:

Traceback (most recent call last):
  File "/apps/sth/projects/IDO/TCaaS/Errbot/errbot/app/venv/lib/python3.4/site-packages/errbot/backends/graphic.py", line 19, in <module>
    from PySide import QtCore, QtGui, QtWebKit
ImportError: No module named 'PySide'
2018-06-11 16:30:44,930 CRITICAL errbot.backends.graphic    To install graphic support use:
    pip install errbot[graphic]

It looks like pytest tries to run Errbot in graphical mode whereas I am using Errbot with a text backend just fine.

As the plugins might need at some point to use the configuration file given to Errbot, I wonder how to do the same while using pytest...