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.
[x] #advanced-search - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/AdvancedSearch/+/932408
[x] #move-files-to-commons ( there's currently only one spec and just a bit JS )
[x] #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 (WIP has issues)
[x] #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 ):
[x] #mediawiki-extensions-codemirror - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CodeMirror/+/934321
[x] #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