There was a task/goal about this, but never a bug that I can find. We had talked about doing this before 1.23, and I still think we should backport browser tests for major core features to the 1.23 branch, since it's an LTS, and isn't too different from master yet.
As background, we currently have no browser tests for our release branched of mediawiki. That has forced us to do a lot of manual testing whenever we release a new version of the tarballs. That's just bad all around.
Chris McMahon put in a first patch 133507. We have a few more features identified in bug 66264. What other features should have basic regression testing?
We briefly discussed having a test for the upgrade process also.