I also had to remove usedevelop = true
from my conf.
My configuration was looking like that:
[tox]
envlist = flake8,py36
[testenv]
usedevelop = true
install_command = pip install -U {opts} {packages}
deps =
py36: -r requirements.txt
py36: -r requirements-test.txt
flake8: flake8
commands=
flake8: flake8 app tests --ignore=E501,W503
py36: pytest {toxinidir}/tests {posargs}
I added skipsdist = true
as the other answers suggest. But it was not enough. As said above, also removing usedevelop = true
did the trick.