Functional test data builder with lambdas and Lombok @wither

gistfile1.java

@Value public class User {

    public final Optional<String> id;
    public final DateTime createdDate;
    public final String firstName;
    public final String lastName;
    @Wither public final Country country;
    @Wither public final PhoneNumber phoneNumber;
    @Wither public final String email;
    @Wither public final Optional<String> stravaId;
    @Wither public final Optional<String> facebookId;

    public User(String id, DateTime createdDate, String firstName, String lastName, Country country, PhoneNumber phoneNumber, String email, Optional<String> stravaId, Optional<String> facebookId) {
        this(Optional.of(id), createdDate, firstName, lastName, country, phoneNumber, email, stravaId, facebookId);
    }
    ...
}


    public static User newUser() {
        return new User("userId", SOME_TIME, "firstName", "lastName", Country.GB, tel("phone"), "email", Ids.NO_ID, Ids.NO_ID);
    }

    public static User newUser(Function<User, User> mapper) {
        return mapper.apply(newUser());
    }
    
// So we can say
User user = Users.newUser(u -> u.withStravaId(Optional.of("stravaId")));