QueryTester's self-tests encounter networking errors to the likes of

Tester exiting after error: Error setting up listener SocketException: /tmp/mongodb-27016.sock\x00 :: caused by :: setup bind :: caused by :: Address already in use

This appears to be caused by a hardcoding of port 27016 when building a connection, causing concurrent QueryTesters running on the same machine to conflict on the same port. Changing this to port 0 should fix the issue, since port 0 will actually just reassign to any available port.