$ tox -av
...
default environments:
py27 -> run test on python2.7
py34 -> run test on python3.4
py35 -> run test on python3.5
py36 -> run test on python3.6
py37 -> run test on python3.7
py38 -> run test on python3.8
py39 -> run test on python3.9
py310 -> run test on python3.10
pypy -> run test on pypy
pypy3 -> run test on pypy3
docs -> mimic readthedocs build
readme -> mimic pypi validation of readme/rst files
black -> show diff of code format