@Override
   public boolean removeAll(IntSet set) {
      throw new UnsupportedOperationException("RangeSet is immutable");
   }
@Test(expected = UnsupportedOperationException.class)
   public void removeAll2() throws Exception {
      RangeSet rs = new RangeSet(4);

      Set<Integer> hashSet = new HashSet<>();

      rs.removeAll(hashSet);
   }