private String validateJSON(String presumablyValidJson) {
        try {
            Jackson.mapper().readTree(presumablyValidJson);
            return "";
        } catch (IOException e) {
            return e.getMessage();
        }
    }
Functional testing of {@link JsonRenderer}.

@author Steinar Knutsen
@author bratseth
container-search/src/test/java/com/yahoo/search/rendering/JsonRendererTestCase.java