indexUpdateCallback.store(paramMap, dataMap);

        // Should keep existing doc_id
        assertEquals("existing-doc-id", dataMap.get("doc_id"));
    }

    @Test
    public void test_concurrentStore() throws Exception {
        // Test thread safety
        final int threadCount = 10;
        final int docsPerThread = 10;
        final List<Thread> threads = new ArrayList<>();