We're planning on using the pluggable nature of RpcControllerFactory to send along custom priorities that are calculated based on some special logic in our stack. Unfortunately it's virtually impossible to test this from user code. On the other hand it's relatively easy to test within the hbase codebase. We should add a test class which verifies for users that this logic works. Then it's just up to them to test their own implementation of their HBaseRpcController rather than do the full integration test.