@Test
 public void testHash() {
   MutableRoaringBitmap rbm1 = new MutableRoaringBitmap();
   rbm1.add(17);
   MutableRoaringBitmap rbm2 = new MutableRoaringBitmap();
   rbm2.add(17);
   Assert.assertTrue(rbm1.hashCode() == rbm2.hashCode());
   rbm2 = rbm1.clone();
   Assert.assertTrue(rbm1.hashCode() == rbm2.hashCode());
 }