//Init bean
User user2 = new User("user2@gmail.com", "Marko", "Vidocic", "user2", true, "Sremska 4, Novi Sad, Srbija");
em.persist(user2);

....
Visit visit2 = new Visit(true,4,reservation1,user2);
em.persist(visit2);
reservation1.addVisit(visit2);
user2.addVisit(visit2);