tox
Another test on current failing build (swh-indexer):
```
(swh-indexer) $ .tox/py3/bin/pip install ../swh-scheduler
(swh-indexer) $ tox -- -x -s
...
330 passed, 15 skipped, 1 warning in 56.79s
-- summary --
black: commands succeeded
flake8: commands succeeded
mypy: commands succeeded
py3: commands succeeded
congratulations :)
```