String value1 = fessConfig.get(testKey);
            assertEquals(initialValue, value1);

            // Change system property
            String newValue = "changed";
            System.setProperty(Constants.FESS_CONFIG_PREFIX + testKey, newValue);

            // Get value again - in real FessConfigImpl it would be cached,
            // but our test implementation always checks system properties

    public void test_overwriteValues() {
        dataStoreParams.put("key1", "originalValue");
        assertEquals("originalValue", dataStoreParams.get("key1"));

        dataStoreParams.put("key1", "newValue");
        assertEquals("newValue", dataStoreParams.get("key1"));

        dataStoreParams.put("key1", null);
        assertNull(dataStoreParams.get("key1"));
    }

    // Test multiple operations in sequence
    @Test