@Override
  public boolean remove(Object o)
  {
    return _map.remove(o) == PRESENT;
  }
@Test
  public void testRemove()
  {
    final CowSet<String> set = new CowSet<>();
    set.add("test");

    Assert.assertTrue(set.remove("test"));
    Assert.assertFalse(set.contains("test"));
    Assert.assertEquals(set.size(), 0);

    Assert.assertFalse(set.remove("test"));
    Assert.assertFalse(set.contains("test"));
    Assert.assertEquals(set.size(), 0);
  }