@Override
            public void onError(Throwable throwable) {
                // This is not called because we didn't specify NOTIFY_CANCELLATION when subscribe.
                fail("unexpected onError()", throwable);
            }
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