See failures at https://gerrit.wikimedia.org/r/#/c/394848/ and https://gerrit.wikimedia.org/r/#/c/394843/ on apparently well-coded patches.
Error is:
1) Wikibase\Repo\Tests\Actions\ViewEntityActionTest::testShowDiff Failed asserting that [... bunch of codes ...] does not contain "wikibase-toolbar-button-edit".