@Override
        public CompletableFuture<DataList<DATATYPE>> completedFuture() {
            synchronized (lock) {
                if (waitForIt == null) {
                    waitForIt = new WrappedFuture<>(super.completedFuture());
                }
            }
            return waitForIt;
        }
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