def test_acceptOutOfFiles(self):
        """
        Test that the platform accept(2) call fails with either L{EMFILE} or
        L{ENOBUFS} when there are too many file descriptors open.
        """
        # Make a server to which to connect
        port = self.socket()
        port.bind(('127.0.0.1', 0))
        serverPortNumber = port.getsockname()[1]
        port.listen(5)

        # Make a client to use to connect to the server
        client = self.socket()
        client.setblocking(False)

        # Use up all the rest of the file descriptors.
        for i in range(self.socketLimit):
            try:
                self.socket()
            except socket.error as e:
                if e.args[0] in (EMFILE, ENOBUFS):
                    # The desired state has been achieved.
                    break
                else:
                    # Some unexpected error occurred.
                    raise
        else:
            self.fail("Could provoke neither EMFILE nor ENOBUFS from platform.")

        # Non-blocking connect is supposed to fail, but this is not true
        # everywhere (e.g. freeBSD)
        self.assertIn(client.connect_ex(('127.0.0.1', serverPortNumber)),
                      (0, EINPROGRESS))

        # Make sure that the accept call fails in the way we expect.
        exc = self.assertRaises(socket.error, port.accept)
        self.assertIn(exc.args[0], (EMFILE, ENOBUFS))

        Test that the platform accept(2) call fails with either L{EMFILE} or
        L{ENOBUFS} when there are too many file descriptors open.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_tcp_internals.py