In trying to load tests/qunit/skins.minerva.notifications.badge/test_NotificationBadge.js the client requests extensions/MinervaNeue/tests/... when in fact the skin in installed in core/skins/MinervaNeue. The resulting 404 causes the page to stop loading. The file loads correctly when resourceLoaderDebug is disabled.
Looks like the tests are explicitly registered with a remote path for extensions/ instead of skins/. Untagging ResourceLoader.
Problematic code is around Minerva.hooks.php#L63 where the FileModule's (localBasePath, remoteBasePath) pair is defined using the remoteExtPath shortcut, instead of the remoteSkinPath shortcut.