'L{TuntapPort.doRead} reads the first part of a datagram of more than
C{TuntapPort.maxPacketSize} from the port\'s file descriptor and passes
the truncated data to its protocol\'s C{datagramReceived} method.'

def test_doReadLargeDatagram(self):

    datagram = ('x' * self.port.maxPacketSize)
    self.port.startListening()
    tunnel = self.system.getTunnel(self.port)
    tunnel.readBuffer.append((datagram + 'y'))
    self.port.doRead()
    self.assertEqual([datagram], self.protocol.received)
