private void buildFactories(AggregatorFactories.Builder factories) throws IOException {
        try (DummyAggregationContext context = new DummyAggregationContext(factories.bytesToPreallocate())) {
            factories.build(context, null).createTopLevelAggregators();
        }
    }

    private class DummyAggregationContext extends AggregationContext {
        private final Query query = new MatchAllDocsQuery();