@Override
 @Test
 public void selectInstancesOf() {
   ImmutableBag<Number> numbers = Bags.immutable.of();
   Assert.assertEquals(iBag(), numbers.selectInstancesOf(Integer.class));
   Assert.assertEquals(iBag(), numbers.selectInstancesOf(Double.class));
   Assert.assertEquals(iBag(), numbers.selectInstancesOf(Number.class));
 }