Would have helped to catch the regression in T284198: Restore/fix vue version of Special:GlobalWatchlist for wvui 0.2.0 earlier - we should test that the non-vue version of the display produces a good output (can check for existence of, eg, the refresh ooui button) and that the vue version of the display produces a good output using wvui (check for a button with the wvui-button class)
Roadmap:
- Figure out how selenium works and what it takes to set up
- Add a placeholder test to make sure the tests are running, eg checking Special:Version for the extension having been loaded properly (cf initial patch at T224903)
- Add tests for OOUI version of the display
- Add tests for Vue version of display (temporarily default $wgGlobalWatchlistDevMode to true to allow overriding which version to use)
- Figure out a better way to allow testing the Vue version without needing to enable dev mode by default, and restore the default to false