private void renderHitGroup(XMLWriter writer, HitGroup hit) throws IOException {
        if (HitRenderer.renderHeader(hit, writer)) {
            // empty
        } else if (hit.types().contains("grouphit")) {
            // TODO Keep this?
            renderHitGroupOfTypeGroupHit(writer, hit);
        } else {
            renderGroup(writer, hit);
        }
    }
Creates an XML renderer using a custom executor.
Using a custom executor is useful for tests to avoid creating new threads for each renderer registry.
container-search/src/main/java/com/yahoo/search/rendering/XmlRenderer.java