I've installed pytest 2.3.4 under Debian Linux.  By default it runs under Python 2.7, but sometimes I'd like to run it under Python 3.x, which is also installed.  I can't seem to find any instructions on how to do that.
The PyPI Trove classifiers show Python :: 3 so presumably it must be possible.  Aside from py.test somedir/sometest.py, I can use python -m pytest ..., or even python2.7 -m pytest ..., but if I try python3 -m pytest ... I get
/usr/bin/python3: No module named pytest
Install it with pip3:
pip3 install -U pytest
Pytest and Python 3