Notes by @hashar:
In MediaWiki, tests are based on webdriver.io which requires nodejs / npm install.
NodeJs on Debian is usually outdated.
We need at least Chromium which is updated on Debian every xx weeks and thus require the container to be rebuild on updates.
To drive Chromium, one need to interact through a proxy chromedriver which is shipped by Chromium (chromedriver --url-base=wd/hub --port=4444)
mediawiki/core tests require ffmpeg to capture video of the test sessions.
Ideally the tests should be run in a different container than the one serving MediaWiki. chromedriver could be in its own container (but most probably has to match the Chromium version) or could be run in the background.