'L{IMAP4Client.fetchSpecific}, when passed C{offset} and C{length},
sends a partial content request (like I{BODY[TEXT]<offset.length>}).
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.'

def test_fetchSpecificPartial(self):

    d = self.client.fetchSpecific('9', headerType='TEXT', offset=17, length=3)
    self.assertEqual(self.transport.value(), '0001    FETCH    9    BODY[TEXT]<17.3>\r\n')
    self.client.lineReceived('*    9    FETCH    (BODY[TEXT]<17>    "foo")')
    self.client.lineReceived('0001    OK    FETCH    completed')
    self.assertEqual(self._extractDeferredResult(d), {9: [['BODY', ['TEXT'], '<17>', 'foo']]})
