The flickering is a symptom of a product bug in the realtime CKEditor plugin, not a test timing problem: the WYSIWYG editor sometimes silently skips joining the realtime collaboration session, because the editor.mode !== 'wysiwyg' guard added by XWIKI-23985 also matches "the editing mode is not set yet". The syntax change makes it likely because the editor is destroyed and recreated while the RequireJS modules and the Netflux WebSocket are already warm, so the realtime bootstrap wins the race.
