assertion error when unittesting persisting objects

I need help understanding why my test is failing.

I'm trying to unittest a persist method for persisting a user. The involwed classes are :

PersistenceManager (singleton for sharing a entitymanagerfactory app wide)

UserControler ( subclass of jpa entity User )

UserActions (junit testclass)

The problem I have is that when I get a entitymanager in the unittest and ask if it contain the just persisted user it returns false.

See below relevant code:

file UserControler:

private EntityManagerFactory emf = PersistenceManager.getInstance().getEntityManagerFactory();
      private EntityManager em;
      
      public User create(String userName,String password,String email,String displayName)
                              throws UserParameterException, UserExistsException, EmailFormatException{
      User user = null;
      
      if(userName==null||password==null||email==null)throw new UserParameterException();
      if(displayName==null)displayName = userName;
      isValidEmail(email);
      
      user = new User();
      String encriptedPassword = encriptPassword(password);
      user.userName = userName;
      user.password = encriptedPassword;
      user.email = email;
      return persistUser(user);
   }

private User persistUser(User user)
   {
      OpenEntityManager();
      em.getTransaction().begin();
      em.persist(user);
      em.getTransaction().commit();
      System.out.println(em.contains(user));
      return user;
   }

private void OpenEntityManager()
   {
      em = emf.createEntityManager();   
   }

file PersistenceManager:
public final class PersistenceManager
{
   
   private static PersistenceManager instance;
   private static EntityManagerFactory emf;
   private PersistenceManager(){}
   
   public static PersistenceManager getInstance(){
      if(instance == null){
         instance = new PersistenceManager();
      }
      return instance;
   }
   
   public EntityManagerFactory getEntityManagerFactory(){
      if(emf == null){
         emf = Persistence.createEntityManagerFactory("blogapp");
      }
      return emf;
   }

}

Unittest file:
   
   @Before
   public void setup(){
      emf = PersistenceManager.getInstance().getEntityManagerFactory();
   }

@Test
   public void testAddNewUser()
   {
      User newUser = null;
      try{
         newUser = new UserControler().create("username", "password", "valid@email.com", "User name");
      }catch(Exception e){
         fail(e.toString());
      }
      dataManager = emf.createEntityManager();
      assertTrue(dataManager.contains(newUser)); // This return false, newUser is valid with id generated with persisting
      
   }

Well,

I resolved the issue, my unittest is passing when i use the find instead of contains.

So that give us a new question:

Given the following scenario:
- jpa persistence with hibernate and H2 transactions configured "resource_local"
- Class A sharing a entityManagerFactory
- Class B getting a entityManager with class A factory and persisting an object Foo

if in a class C we get a entityManager with class A factory and query for Foo:
- contains return false
- find returns object foo as expected.

Can somebody explain what i'm missing to understand here?