public void error(XMLWriter writer, Result result) throws IOException {
        ErrorMessage error = result.hits().getError();
        writer.openTag(ERROR).attribute(CODE,error.getCode()).content(error.getMessage(),false).closeTag();
    }
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