@Test
public void testBackwardCompatibility() {

    KylinConfig config = KylinConfig.getInstanceFromEnv();
    final String oldk = "kylin.test.bcc.old.key";
    final String newk = "kylin.test.bcc.new.key";
    assertNull(config.getOptional(oldk));
    assertNotNull(config.getOptional(newk));
    Map<String, String> override = Maps.newHashMap();
    override.put(oldk, "1");
    KylinConfigExt ext = KylinConfigExt.createInstance(config, override);
    assertEquals(ext.getOptional(oldk), null);
    assertEquals(ext.getOptional(newk), "1");
    assertNotEquals(config.getOptional(newk), "1");
    config.setProperty(oldk, "2");
    assertEquals(config.getOptional(newk), "2");
}