'Create the protocol instance, keeps track of it, and makes it use
C{clientFactoryInstance} as client factory.'

def buildProtocol(self, addr):

    proto = portforward.ProxyFactory.buildProtocol(self, addr)
    self.clientFactoryInstance = TestableProxyClientFactory()
    proto.clientProtocolFactory = (lambda : self.clientFactoryInstance)
    self.protoInstance = proto
    return proto
