@Override
        public void onSubscribe(Subscription s) {
            subscription = s;
            s.request(demand);
        }
A test for the {@link SignalQueue} in {@link DefaultStreamMessageDuplicator}.
Queue expansion behaves differently when odd/even number head wrap-around happens.
core/src/test/java/com/linecorp/armeria/common/stream/StreamMessageDuplicatorTest.java