public void testCount_elementPresent() {
    int COUNT = 12;
    when(backingMap.get(KEY)).thenReturn(new AtomicInteger(COUNT));

    assertEquals(COUNT, multiset.count(KEY));
  }

  public void testCount_elementAbsent() {
    when(backingMap.get(KEY)).thenReturn(null);

    assertEquals(0, multiset.count(KEY));
  }

  public void testAdd_zero() {
    int INITIAL_COUNT = 32;