when(backingMap.remove(KEY, current)).thenReturn(true);

    assertEquals(countToRemove, multiset.setCount(KEY, 0));
    assertEquals(0, current.get());
  }

  public void testSetCount_0_nonePresent() {
    when(backingMap.get(KEY)).thenReturn(null);

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

  public void testSerialCycle() {