@Override
    public long putIfAbsent(K key, long newValue) {
        return complete(asyncCounterMap.putIfAbsent(key, newValue));
    }
@Test
    public void testPutIfAbsent() {
        atomicCounterMap.putIfAbsent(KEY1, VALUE1);
        Long afterIncrement = atomicCounterMap.addAndGet(KEY1, DELTA1);
        assertThat(afterIncrement, is(VALUE1 + DELTA1));
    }