ObjectStore os = ObjectStore.Factory.create();
os.register(B1.class.getSimpleName(), B1.class);
os.register(B2.class.getSimpleName(), B2.class);
Key key = os.beginSession().store(a).now();
A a2 = os.beginSession().load(key).now();
assertEquals(a, a2);
Entity e = DatastoreServiceFactory.getDatastoreService().get(key);
assertEquals(Lists.newArrayList(null, "B1", "B2"), e.getProperty("bs.contents.__type__"));
assertEquals(Lists.newArrayList("Fred", "Bob", "Schmoo"), e.getProperty("bs.contents.x"));