@Nullable
    @Override
    public Void answer(InvocationOnMock invocation) throws Throwable {
      Consumer consumer = (Consumer) invocation.getArguments()[0];
      Iterator<CloseableReference<CloseableImage>> iterator = mResults.iterator();
      while (iterator.hasNext()) {
        CloseableReference<CloseableImage> result = iterator.next();
        consumer.onNewResult(result, BaseConsumer.simpleStatusForIsLast(!iterator.hasNext()));
      }
      return null;
    }
Checks basic properties of swallow result producer, that is: - it swallows all results. - it
notifies previous consumer of last result. - it notifies previous consumer of a failure.
imagepipeline/src/test/java/com/facebook/imagepipeline/producers/SwallowResultProducerTest.java