I just tried writing tests for it, but I don't know idlelib/rpc.py
enough yet. You can see this first attempt at:
http://svn.python.org/view?view=rev&revision=74320

I started trying to test rpc.RPCClient together with run.main but it
seemed too high level. Then I moved to try to test rpc.SocketIO
directly, but it seems I'm doing wrong things there. Most of times
SocketIOTest will fail by raising ValueError which then causes the
server process to finish and either cause a "Connection reset by peer",
"Broken pipe" or nothing (these are on Linux, on Windows I would expect
to get "An existing connection was forcibly closed by the remote host").
Sometimes it also succeeds.