def test_fetchSpecific(self):
        """
        L{IMAP4Client.fetchSpecific} sends the I{BODY[]} command if no
        parameters beyond the message set to retrieve are given.  It returns a
        L{Deferred} which fires with a C{dict} mapping message sequence numbers
        to C{list}s of corresponding message data given by the server's
        response.
        """
        d = self.client.fetchSpecific('7')
        self.assertEqual(
            self.transport.value(), b'0001 FETCH 7 BODY[]\r\n')
        self.client.lineReceived(b'* 7 FETCH (BODY[] "Some body")')
        self.client.lineReceived(b'0001 OK FETCH completed')
        self.assertEqual(
            self.successResultOf(d), {7: [['BODY', [], "Some body"]]})

        L{IMAP4Client.fetchSpecific} sends the I{BODY[]} command if no
        parameters beyond the message set to retrieve are given.  It returns a
        L{Deferred} which fires with a C{dict} mapping message sequence numbers
        to C{list}s of corresponding message data given by the server's
        response.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py