final PhoneBook modifiedPhoneBook = PhoneBook.from(phoneBook);
modifiedPhoneBook.getContact("Jesse", "Pinkman").setMiddleName("Bruce");
modifiedPhoneBook.getContact("Walter", "White").setMiddleName("Hartwell");
final ObjectDiffer objectDiffer = ObjectDifferBuilder.buildDefault();
final DiffNode node = objectDiffer.compare(modifiedPhoneBook, phoneBook);
assertThat(node.hasChanges(), is(true));
assertThat(node.hasChildren(), is(true));
assertThat(node.childCount(), is(1));