final String endpointToken2 = extractEndpointToken(registerResponse2.getPushEndpoint());
server.handleNotification(endpointToken1, "version=10");
server.handleNotification(endpointToken2, "version=23");
final Ack ackChannel_1 = new AckImpl(channelId_1, 10L);
final Set<Ack> unacked = server.handleAcknowledgement(new AckMessageImpl(asSet(ackChannel_1)), uaid);
assertThat(unacked, hasItem(new AckImpl(channelId_2, 23L)));
}