store.saveChannel(channel2);
store.saveUnacknowledged(channel1.getChannelId(), channel1.getVersion());
store.saveUnacknowledged(channel2.getChannelId(), channel2.getVersion());
final Set<Ack> acks = asSet(new AckImpl(channel1.getChannelId(), channel1.getVersion()));
final Set<Ack> unacknowledged = store.removeAcknowledged(channel1.getUAID(), acks);
assertThat(unacknowledged.size(), is(1));
assertThat(unacknowledged, hasItem(new AckImpl(channel2.getChannelId(), channel2.getVersion())));
}