See https://www.mediawiki.org/wiki/Selenium for how to best run these locally. Below the internal prerequisites are documented, but you might not need to install these yourself.
There are three supported modes of running the tests.
The Selenium tests default to headless mode, unless a DISPLAY environment variable is set. This variable may be set on Linux desktop and XQuartz environments. To run headless there, unset the DISPLAY environment variable first.
npm run selenium-test
Or:
DISPLAY= npm run selenium-test
To see the browser window, ensure the DISPLAY variable is set. On Linux desktop and in XQuartz environments this is probably set already. On macOS, set it to a dummy value like 1.
DISPLAY=1 npm run selenium-test
To capture a video, the tests have to run in the context of an X11 server, with the DISPLAY environment variable set to its display name. If the shell has no X11 server or if you want to hide the output, you can also launch a virtual X11 display using Xvfb. Recording videos is currently supported only on Linux, and is triggered by the DISPLAY value starting with a colon (as Xvfb typically would).
Example test run in Fresh.
fresh-node -env -net export DISPLAY=:1 Xvfb "$DISPLAY" -screen 0 1280x1024x24 & npm run selenium-test
Run a specific spec:
npm run selenium-test -- --spec tests/selenium/specs/page.js
To filter by test case, e.g. with the name containing "preferences":
npm run selenium-test -- --mochaOpts.grep preferences
The following environment variables decide where to find MediaWiki and how to login:
MW_SERVER: The value of $wgServer.MW_SCRIPT_PATH: The value of $wgScriptPath.MEDIAWIKI_USER: Username of a wiki account with sysop rights.MEDIAWIKI_PASSWORD: Password for this user.