static void serialize(Map<String, Object> m, JSONWriter w) throws IOException {
            w.beginObject();
            for (Map.Entry<String, Object> e : m.entrySet()) {
                w.beginField(e.getKey());
                final Object value = e.getValue();
                serializeField(w, value);
                w.endField();
            }
            w.endObject();
        }
Object identity is used to differentiate between different implementation strategies, toString() is used to print a report.

@return an object with a descriptive toString() for the implementation under test
vespajlib/src/test/java/com/yahoo/text/JsonMicroBenchmarkTestCase.java