return auto generated ids

persistence-modules/java-jpa-3/src/test/java/com/baeldung/jpa/IdGeneration/IdGenerationIntegrationTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.jpa.IdGeneration;
+
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import java.util.UUID;
+
+public class IdGenerationIntegrationTest {
+
+    private static EntityManager entityManager;
+    private static UserService service;
+
+    @BeforeClass
+    public static void setup() {
+        EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-h2-id-generation");
+        entityManager = factory.createEntityManager();
+        service = new UserService(entityManager);
+    }
+
+    @Test
+    public void whenNewUserIsPersisted_thenEntityHasNoId() {
+        User user = new User();
+        user.setUsername("test");
+        user.setPassword(UUID.randomUUID().toString());
+
+        long index = service.saveUser(user);
+        Assert.assertEquals(0L, index);
+    }
+
+    @Test
+    public void whenTransactionIsControlled_thenEntityHasId() {
+        User user = new User();
+        user.setUsername("test");
+        user.setPassword(UUID.randomUUID().toString());
+
+        entityManager.getTransaction().begin();
+        long index = service.saveUser(user);
+        entityManager.getTransaction().commit();
+
+        Assert.assertEquals(2L, index);
+    }
+
+}