The problem if that we need the behaviour of those two methods from the real transport, but we don't want to actually use the whole thing here. Fixing that would require rewriting quite a lot of the tests.

All this code does is copy those methods from the real transport. It has to grab the underlying function objects because the unbound method objects (which is what you get from `SmppTransceiverTransport.get_sequence_number_message_id`) check the type of the first parameter. I could replace this with a wrapper function that calls the functions, but that's basically just a more verbose version of the same thing.