Map<String, Object> dataMap = new HashMap<>();
        dataMap.put("a", "A0");
        Map<String, Object> responseDataMap = new HashMap<>();
        responseDataMap.put("b", "B1");

        indexUpdateCallback.mergeResponseData(dataMap, responseDataMap);

        assertEquals(2, dataMap.size());
        assertEquals("A0", dataMap.get("a"));
        assertEquals("B1", dataMap.get("b"));
    }