Provide a way to run a single test module or function

[allan-silva]

Sometimes it's useful run a single test module or function, without run the entire test suite, mainly on development time.

There's no obvious way to do it currently.

Edit:
I was able to test a module, running the image in interactive mode:

docker run --rm -it --mount type=bind,source="$(pwd)",target=/app -v balrog_backend-docker-tox:/app/.tox -e TOXENV=py38 --entrypoint /bin/bash balrog_backend-docker-test

root@1921b24100a9:/app# py.test tests/test_AUS.py