def test_fetchUID(self):
        """
        L{IMAP4Client.fetchUID} sends the I{FETCH UID} command and returns a
        L{Deferred} which fires with a C{dict} mapping message sequence numbers
        to C{dict}s mapping C{'UID'} to that message's I{UID} in the server's
        response.
        """
        d = self.client.fetchUID('1:7')
        self.assertEqual(self.transport.value(), b'0001 FETCH 1:7 (UID)\r\n')
        self.client.lineReceived(b'* 2 FETCH (UID 22)')
        self.client.lineReceived(b'* 3 FETCH (UID 23)')
        self.client.lineReceived(b'* 4 FETCH (UID 24)')
        self.client.lineReceived(b'* 5 FETCH (UID 25)')
        self.client.lineReceived(b'0001 OK FETCH completed')
        self.assertEqual(
            self.successResultOf(d), {
                2: {'UID': '22'},
                3: {'UID': '23'},
                4: {'UID': '24'},
                5: {'UID': '25'}})

        L{IMAP4Client.fetchUID} sends the I{FETCH UID} command and returns a
        L{Deferred} which fires with a C{dict} mapping message sequence numbers
        to C{dict}s mapping C{'UID'} to that message's I{UID} in the server's
        response.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py