[Twisted-Python] cfreactor and global state

twisted.internet.test.reactormixins says: CFReactor uses APIs which manipulate global state, so it's not safe to run its own reactor-builder tests under itself. We also don't have a buildslave running under cfreactor. Which means it's currently completely untested. I filed a ticket to fix that - https://bugs.launchpad.net/twisted-buildbot-configuration/+bug/954680 That still leaves the problem with global state though. Since we want to move towards having tests create new reactors, that's problematic. What global state does it manipulate, and what can we do about it?