public long size() {
    return counters.size();
  }
@Test
  public void testAddWithAlreadyPresentNameReturnsFalse() {
    Counter<?, ?> c1 = counterSet.longSum(name1);
    Counter<?, ?> c1Dup = counterSet.longSum(name1);

    assertSame(c1, c1Dup);
    assertThat(counterSet.size(), equalTo(1L));
  }