Ok this comes from when you cannot download chromedriver and no tests runs. I can add a check so we don't try to store the file if no tests runs.

Change #1197391 had a related patch set uploaded (by Phedenskog; author: Phedenskog):

[mediawiki/core@master] selenium: Only write Promethues metrics if test runs

https://gerrit.wikimedia.org/r/1197391

I think this must have been introduced with the 6.0.0 release?

I don’t think so, I’m also encountering it in this Wikibase change that’s just upgrading to wdio-mediawiki v4. It might be a different underlying issue that causes the metricsDir to not contain any specs-*.json files?

Do you know if it would be possible to backport the fix to wdio-mediawiki v4 and v5? Or to work around it in another way on those versions?

Workaround for wdio.conf.js (where config is imported from wdio-mediawiki/wdio-defaults.conf.js):

onComplete() {
	try {
		return config.onComplete();
	} catch ( _ ) {
		// ignore TypeError: Cannot read properties of undefined (reading 'project') [T407831]
		// remove this onComplete() override again once we’re on a version of wdio-mediawiki
		// with a fix (maybe 6.0.1?)
	}
}

Change #1197391 merged by jenkins-bot:

[mediawiki/core@master] selenium: Only write Promethues metrics if test runs

https://gerrit.wikimedia.org/r/1197391

Change #1211178 had a related patch set uploaded (by Lucas Werkmeister (WMDE); author: Lucas Werkmeister (WMDE)):

[mediawiki/extensions/Wikibase@master] WIP: Remove workaround for T407831

https://gerrit.wikimedia.org/r/1211178