Currently when a ShardingTest is setup under auth passthrough, if the shard is a replica set an admin user for use by the auth passthrough system gets added to the shard primary. If the shard is a standalone or master/slave, however, the admin user doesn't get added. This means that if the test tries to make a direct connection to the shard and do anything, it will get "unauthorized" errors as the auth system was unable to authenticate the connection since no admin user exists.