public void testClone() throws Exception {
    DrillDownQuery q = new DrillDownQuery(config, new MatchAllDocsQuery());
    q.add("a");

    DrillDownQuery clone = q.clone();
    clone.add("b");

    assertFalse(
        "query wasn't cloned: source=" + q + " clone=" + clone,
        q.toString().equals(clone.toString()));
  }