@Override
   public boolean add(Integer integer) {
      throw new UnsupportedOperationException("RangeSet is immutable");
   }
@Test
   public void equals2() throws Exception {
      IntSet rs = new RangeSet(4);

      Set<Integer> hashSet = new HashSet<>();
      hashSet.add(0);
      hashSet.add(1);
      hashSet.add(2);

      // Verify equals both ways
      assertNotEquals(rs, hashSet);
      assertNotEquals(hashSet, rs);

      hashSet.add(3);

      assertEquals(rs, hashSet);
      assertEquals(hashSet, rs);
   }