@Override
        public void onComplete() {}
This test checks that the duplicator does not release the elements that it holds until all subscribers are
received all element via {@link Subscriber#onNext(Object)}.
Previously, the duplicator has a bug that releases the elements when the duplicator is closed even though
there's a subscriber that does not subscribe to the child stream message yet.
See <a href="https://github.com/line/armeria/pull/3337">
Fix not to release elements before subscribed in duplicator</a>
core/src/test/java/com/linecorp/armeria/common/stream/StreamMessageDuplicatorCloseTest.java