EntityDataRequestHandlerTest::testCacheHeaderIsSetWithRevision seems to fail consistently on Travis CI build.
Example failed test output
There was 1 failure: 1) Wikibase\Repo\Tests\LinkedData\EntityDataRequestHandlerTest::testCacheHeaderIsSetWithRevision Failed asserting that 'private, no-cache, s-maxage=0' contains "public". /home/travis/build/wikimedia/phase3/extensions/Wikibase/repo/tests/phpunit/includes/LinkedData/EntityDataRequestHandlerTest.php:376 /home/travis/build/wikimedia/phase3/tests/phpunit/MediaWikiIntegrationTestCase.php:437 /home/travis/build/wikimedia/phase3/maintenance/doMaintenance.php:107
This has started with https://travis-ci.org/github/wikimedia/mediawiki-extensions-Wikibase/builds/729185727 triggered by merging https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/621757
Possibly relevant, possibly not, the failed tests happen in environments where wiki language is not English.