No colors by default on GitHub Actions

When running pytest on GitHub Actions (like we do ourselves, random example), the output is not colored.

pytest does color output on Travis CI by default, so it could be argued that this is somehow GitHub Action’s fault. However, other tools (e.g. eslint, and I think mypy) seem to colorize their output on GitHub actions just fine, without needing to force them! From what I’ve seen, those tools seem to be influenced by the TERM environment variable, while pytest’s (or pylib’s?) autodetection seems to work differently?

As a workaround, this helps (as part of the step definition):

      - name: "Run pytest"
        env:
          PYTEST_ADDOPTS: "--color=yes"
        run: pytest

(If you run pytest via tox, make sure to add PYTEST_ADDOPTS to passenv!)

[nicoddemus]

Thanks @jhol and @eine for bringing this up. I’ve created #7464 to track adding this support to pytest. 👍

[jhol]

NO_COLOR is a community standard environement variable.

The general behavior is:

• A command line application emits colour when attached to a TTY, but no colour otherwise e.g. when attached to a pipe.
• NO_COLOR stops the application from emitting colour even when attached to a TTY
• My extension to the standard is to add FORCE_COLOR which forces the application to emit colour escape sequences even when not outputting to a TTY e.g. if we want to pipe into a log file with colour.