def test_startLoggingTwice(self):
        """
        There are some obscure error conditions that can occur when logging is
        started twice. See http://twistedmatrix.com/trac/ticket/3289 for more
        information.
        """
        self._startLoggingCleanup()
        # The bug is particular to the way that the t.p.log 'global' function
        # handle stdout. If we use our own stream, the error doesn't occur. If
        # we use our own LogPublisher, the error doesn't occur.
        sys.stdout = StringIO()

        def showError(eventDict):
            if eventDict['isError']:
                sys.__stdout__.write(eventDict['failure'].getTraceback())

        log.addObserver(showError)
        self.addCleanup(log.removeObserver, showError)
        observer = log.startLogging(sys.stdout)
        self.addCleanup(observer.stop)
        # At this point, we expect that sys.stdout is a StdioOnnaStick object.
        self.assertIsInstance(sys.stdout, LoggingFile)
        fakeStdout = sys.stdout
        observer = log.startLogging(sys.stdout)
        self.assertIs(sys.stdout, fakeStdout)

        There are some obscure error conditions that can occur when logging is
        started twice. See http://twistedmatrix.com/trac/ticket/3289 for more
        information.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_log.py