def test_loggingFactoryOpensLogfileAutomatically(self):
        """
        When the L{policies.TrafficLoggingFactory} builds a protocol, it
        automatically opens a unique log file for that protocol and attaches
        the logfile to the built protocol.
        """
        open_calls = []
        open_rvalues = []

        def mocked_open(*args, **kwargs):
            """
            Mock for the open call to prevent actually opening a log file.
            """
            open_calls.append((args, kwargs))
            io = NativeStringIO()
            io.name = args[0]
            open_rvalues.append(io)
            return io

        self.patch(builtins, 'open', mocked_open)

        wrappedFactory = protocol.ServerFactory()
        wrappedFactory.protocol = SimpleProtocol
        factory = policies.TrafficLoggingFactory(wrappedFactory, 'test')
        first_proto = factory.buildProtocol(address.IPv4Address('TCP',
                                                                '127.0.0.1',
                                                                12345))
        second_proto = factory.buildProtocol(address.IPv4Address('TCP',
                                                                 '127.0.0.1',
                                                                 12346))

        # We expect open to be called twice, with the files passed to the
        # protocols.
        first_call = (('test-1', 'w'), {})
        second_call = (('test-2', 'w'), {})
        self.assertEqual([first_call, second_call], open_calls)
        self.assertEqual(
            [first_proto.logfile, second_proto.logfile], open_rvalues
        )

        When the L{policies.TrafficLoggingFactory} builds a protocol, it
        automatically opens a unique log file for that protocol and attaches
        the logfile to the built protocol.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_policies.py