public void clear() {
    getProps().clear();
    getOverlay().clear();
  }
@Test
  public void testClear() {
    Configuration conf = new Configuration(false);
    conf.set("a", "A");
    conf.set("b", "B");
    conf.clear();
    assertEquals(0, conf.size());
    assertFalse(conf.iterator().hasNext());
  }