How to disconnect w/ Twisted cleanly?

gistfile1.py

from twisted.internet import protocol, reactor
from twisted.words.protocols import irc
from twisted.internet.endpoints import TCP4ClientEndpoint



class TestProtocol(irc.IRCClient):
  nickname = 'test098765'

  def signedOn(self):
    self.join('##test098765')



class TestFactory(protocol.ClientFactory):
  protocol = TestProtocol


  def clientConnectionLost(self, connector, reason):
    print 'I am never called.'



class Test(object):
  def __init__(self):
    self.protocol = None

    reactor.addSystemEventTrigger('before', 'shutdown', self._shutdown)


  def go(self):
    endpoint = TCP4ClientEndpoint(reactor, 'irc.freenode.net', 6667)

    factory = TestFactory()
    d = endpoint.connect(factory)
    d.addCallbacks(self._callback_connected, self._callback_error)

    reactor.run()


  def _callback_connected(self, protocol):
    self.protocol = protocol


  def _callback_error(self, reason):
    raise Exception(reason)


  def _shutdown(self):
    self.protocol.quit('Goodbye IRC...')



if __name__ == "__main__":
  t = Test()
  t.go()