private byte[] completeDocString(String operation, String docId, String fields) {
        return Utf8.toBytes("{\"" + operation + "\": \"" + docId + "\", \"fields\": " + fields + "}");
    }
Functional tests for com.yahoo.document.json.JsonWriter.

@author Steinar Knutsen
document/src/test/java/com/yahoo/document/json/JsonWriterTestCase.java