Add a JPA-complaint contains test to assert the use case descriebed in the following forum thread

https://forum.hibernate.org/viewtopic.php?f=1&t=1044231

hibernate-core/src/test/java/org/hibernate/jpa/test/ops/ContainsTest.java

@@ -0,0 +1,62 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.jpa.test.ops;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
+
+import org.junit.Test;
+
+import static org.hibernate.testing.transaction.TransactionUtil.doInJPA;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * @author Vlad Mihalcea
+ */
+public class ContainsTest extends BaseEntityManagerFunctionalTestCase {
+
+	@Override
+	protected Class<?>[] getAnnotatedClasses() {
+		return new Class<?>[] {
+				Person.class,
+		};
+	}
+
+	@Test
+	public void testLifecycle() {
+		Person _person = doInJPA( this::entityManagerFactory, entityManager -> {
+			Person person = new Person();
+			person.id = 1L;
+			person.name = "John Doe";
+			entityManager.persist( person );
+
+			assertTrue(entityManager.contains( person ));
+
+			return person;
+		} );
+		doInJPA( this::entityManagerFactory, entityManager -> {
+			assertFalse(entityManager.contains( _person ));
+
+			Person person = entityManager.find( Person.class, 1L );
+
+			assertTrue(entityManager.contains( person ));
+		} );
+	}
+
+	@Entity(name = "PersonEntity")
+	public static class Person {
+
+		@Id
+		private Long id;
+
+		private String name;
+	}
+
+}