Tips

To run tests

Install requirements: pip install -r test-requirements.txt (possibly in a virtualenv)
Actually run the tests: pytest tests

To run yapf

Show what changes yapf wants to make: yapf -rpd setup.py src tests
Apply all changes directly to the source tree: yapf -rpi setup.py src tests

To make a release

Update the version in outcome/_version.py
Run towncrier to collect your release notes.
Review your release notes.
Check everything in.
Double-check it all works, docs build, etc.
Build your sdist and wheel: python setup.py sdist bdist_wheel
Upload to PyPI: twine upload dist/*
Use git tag to tag your version.
Don't forget to git push --tags.