Apparently some PHPUnit tests of BetaFeatures are failing. See e.g. https://integration.wikimedia.org/ci/job/mwext-testextension-php55-composer/8198/console (it is a Jenkins build for Wikibase patch, Wikibase pulls in BetaFeatures).
It loooks like the extension itself hasn't really changed recently. Apparently some recent improvement ins OOJS UI might have caused the test failure. I haven't tracked down the particular change there (maybe https://gerrit.wikimedia.org/r/#/c/332398/ /) but I don't think it is really important here what made those tests fail.
https://gerrit.wikimedia.org/r/#/c/336599/ is a rather simple and no-brain-involved way to fix those tests.
BTW: those tests, the way there are now, seem quite fragile. Whenever OO adds/changes some HTML attributes, they are going to fail. I believe even if attribute order changes test are going to break. Maybe it would be worth changing them in such a way that only really important bits of HTML are checked? I am not very familiar with this extension, so I'd like to decide myself what attributes etc can be left over and so on.