Xvfb makes fake X11 for CI

Continuous integration for program that plot or need a display can be tricky, since in many cases the CI doesn’t have an X11 display server. Workarounds include generating plots using X server virtual framebuffer (Xvfb) dummy X11 display server. This maintains code coverage and may allow dumping plots to disk for further checks

GitHub Actions: “.github/workflows/ci.yml”: assuming the project uses PyTest, the xvfb-action enables Xvfb for that command:

- name: Run headless test
  uses: GabrielBB/xvfb-action
    run: pytest

Related: Detect CI via environment variable](/ci-detect-environment-variable)