'If the user requests the TestSubsystem subsystem, connect them to a
MockProtocol.  If they request neither, then None is returned which is
interpreted by SSHSession as a failure.'

def lookupSubsystem(self, name, data):

    if (name == 'TestSubsystem'):
        self.subsystem = MockProtocol()
        self.subsystem.packetData = data
        return self.subsystem
