'When timeouts occur waiting for responses to queries, the next
configured server is issued the query.  When the query has been issued
to all configured servers, the timeout is increased and the process
begins again at the beginning.'

def test_roundRobinBackoff(self):

    addrs = [(x, 53) for x in self.testServers]
    r = client.Resolver(resolv=None, servers=addrs)
    proto = FakeDNSDatagramProtocol()
    r._connectedProtocol = (lambda : proto)
    return r.lookupAddress('foo.example.com').addCallback(self._cbRoundRobinBackoff).addErrback(self._ebRoundRobinBackoff, proto)
