First, thanks for tox. It is very useful.
I have a setuptools-based setup.py with install_requires, setup_requires and tests_require. I was surprised to find that I needed to duplicate the test dependencies in tox.ini; I checked the doc and many examples from projects I follow and finally asked for confirmation on IRC. Ronny suggested that I report this.
IMO, tox should fetch setup_requires and tests_require dependencies too. This would certainly shorten a lot of people’s tox.ini :)