@Override
   public PrimitiveIterator.OfInt iterator() {
      return new SingleIntIterator();
   }
@Test
   public void testIterator() throws Exception {
      IntSet sis = new SingletonIntSet(3);
      PrimitiveIterator.OfInt iterator = sis.iterator();
      assertEquals(3, iterator.nextInt());
      assertFalse(iterator.hasNext());
   }