public void testImmutableEnumSet_deserializationMakesDefensiveCopy() throws Exception {
    ImmutableSet<SomeEnum> original = Sets.immutableEnumSet(SomeEnum.A, SomeEnum.B);
    int handleOffset = 6;
    byte[] serializedForm = serializeWithBackReference(original, handleOffset);
    ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(serializedForm));