In theory it should be possible to trigger parallel execution of specs by adding a line to the wdio.conf.js e.g. [1]. Let's try to do that for the extensions we care about most.
- Advanced-Search - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/AdvancedSearch/+/932408
- Move-Files-To-Commons ( there's currently only one spec and just a bit JS )
- Revision-Slider - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/RevisionSlider/+/932407
- Two-Column-Edit-Conflict-Merge - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/TwoColConflict/+/932409 ( blocked by T340943: TwoColConflict selenium tests run in parallel trigger db errors )
- Electron-PDFs ( there's only one spec file so I think it's not working there )
Optional bonus material ( because we mainly touched the browser tests there last ):
- MediaWiki-extensions-CodeMirror - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CodeMirror/+/934321
- Page-Previews - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Popups/+/934271
[1] https://gerrit.wikimedia.org/r/c/mediawiki/skins/MinervaNeue/+/751767/2/tests/selenium/wdio.conf.js