'When C{requireTransportSecurity} is C{True} and the client is connected
over a non-SSL transport, if the server offers the I{STARTTLS}
extension, it is used before mail is delivered.'

def test_requireTransportSecurityTLSOffered(self):

    transport = StringTransport()
    self.clientProtocol.makeConnection(transport)
    self.clientProtocol.dataReceived(self.SERVER_GREETING)
    transport.clear()
    self.clientProtocol.dataReceived((self.EHLO_RESPONSE + '250-AUTH    LOGIN\r\n250    STARTTLS\r\n'))
    self.assertEqual('STARTTLS\r\n', transport.value())
