You can get Pytest to run your Nosetests so I think you can just merge this as-is. See https://docs.pytest.org/en/6.2.x/nose.html for more.
Off-topic: does capsul do tagged releases? That'd be handy as the plugins/docker plugin has a auto_tag: true which generates the image tag based on the git tag. That is probably One For Later ™️
Feel free to ignore but I usually add --no-cache to save space and newline + sort things so it is easier to have a visual overview of dependencies and alphabetic ordering to know where to slot things in. Can be useful if you end up adding a lot of dependencies and then need to remove them over time as the software changes.
Same totally optional comment as https://git.autonomic.zone/3wordchant/capsul-flask/pulls/2/files#issuecomment-7607.
Optional: var = os.environ.get(f"{var_name}_FILE") also works as it defaults to None if missing.
Maybe postgres:9.6-alpine as it is smaller? https://hub.docker.com/_/postgres?tab=description&page=1&ordering=last_updated
Fantastic work! All of my comments are mostly rambly commentary on not-necessary changes at all unless you feel like it. I had a glass of wine and I was enjoying typing. You'll have to forgive me.
