@Override
        public CompletableFuture<F> whenCompleteAsync(BiConsumer<? super F, ? super Throwable> action, Executor executor) {
            wrapped.whenCompleteAsync(action);
            isListening.put(Boolean.TRUE);
            return this;
        }
Test adding hits to a hit group during rendering.

@author <a href="mailto:steinar@yahoo-inc.com">Steinar Knutsen</a>
container-search/src/test/java/com/yahoo/search/rendering/AsyncGroupPopulationTestCase.java