'If a UDP datagram is sent to an address reachable by the tunnel device
then it can be read out of the tunnel device.'

def test_receive(self):

    parse = self.helper.parser()
    found = False
    for i in range(100):
        key = randrange((2 ** 64))
        message = ('hello    world:' + intToBytes(key))
        source = self.system.sendUDP(message, (self._TUNNEL_REMOTE, 12345))
        for j in range(100):
            try:
                packet = self.system.read(self.fileno, 1024)
            except EnvironmentError as e:
                if (e.errno in (EAGAIN, EWOULDBLOCK)):
                    break
                raise
            else:
                datagrams = parse(packet)
                if ((message, source) in datagrams):
                    found = True
                    break
                del datagrams[:]
        if found:
            break
    if (not found):
        self.fail('Never    saw    probe    UDP    packet    on    tunnel')
