HHH-7404 HHH-6776 Add tests to prevent regressions

The issues have apparently already been fixed but let's add the tests
present in the issue to prevent regressions.

hibernate-core/src/test/java/org/hibernate/test/onetomany/OneToManyDuplicateInsertionTest.java

@@ -0,0 +1,194 @@
+/*
+ * 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.test.onetomany;
+
+import static org.hibernate.testing.transaction.TransactionUtil.doInJPA;
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+import javax.persistence.CascadeType;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.ManyToOne;
+import javax.persistence.OneToMany;
+
+import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
+import org.hibernate.testing.TestForIssue;
+import org.junit.Test;
+
+public class OneToManyDuplicateInsertionTest extends BaseEntityManagerFunctionalTestCase {
+
+	private int parentId;
+
+	@Override
+	protected Class<?>[] getAnnotatedClasses() {
+		return new Class<?>[]{ Parent.class, Child.class, ParentCascade.class, ChildCascade.class };
+	}
+
+	@Test
+	@TestForIssue(jiraKey = "HHH-6776")
+	public void testDuplicateInsertion() {
+		// persist parent entity in a transaction
+
+		doInJPA( this::entityManagerFactory, em -> {
+			Parent parent = new Parent();
+			em.persist( parent );
+			parentId = parent.getId();
+		} );
+
+		// relate and persist child entity in another transaction
+
+		doInJPA( this::entityManagerFactory, em -> {
+			Parent parent = em.find( Parent.class, parentId );
+			Child child = new Child();
+			child.setParent( parent );
+			parent.getChildren().add( child );
+			em.persist( child );
+
+			assertEquals( 1, parent.getChildren().size() );
+		} );
+
+		// get the parent again
+
+		doInJPA( this::entityManagerFactory, em -> {
+			Parent parent = em.find( Parent.class, parentId );
+
+			assertEquals( 1, parent.getChildren().size() );
+		} );
+	}
+
+	@Test
+	@TestForIssue(jiraKey = "HHH-7404")
+	public void testDuplicateInsertionWithCascadeAndMerge() {
+		doInJPA( this::entityManagerFactory, em -> {
+			ParentCascade p = new ParentCascade();
+			// merge with 0 children
+			p = em.merge( p );
+			parentId = p.getId();
+		} );
+
+		doInJPA( this::entityManagerFactory, em -> {
+			ParentCascade p = em.find( ParentCascade.class, parentId );
+			final ChildCascade child = new ChildCascade();
+			child.setParent( p );
+			p.getChildren().add( child );
+			em.merge( p );
+		} );
+
+		doInJPA( this::entityManagerFactory, em -> {
+			// again, load the Parent by id
+			ParentCascade p = em.find( ParentCascade.class, parentId );
+
+			// check that we have only 1 element in the list
+			assertEquals( 1, p.getChildren().size() );
+		} );
+	}
+
+	@Entity(name = "Parent")
+	public static class Parent {
+
+		@Id
+		@GeneratedValue
+		private int id;
+
+		@OneToMany(mappedBy = "parent")
+		private List<Child> children = new LinkedList<Child>();
+
+		public int getId() {
+			return id;
+		}
+
+		public void setId(int id) {
+			this.id = id;
+		}
+
+		public List<Child> getChildren() {
+			return children;
+		}
+
+		public void setChildren(List<Child> children) {
+			this.children = children;
+		}
+	}
+
+	@Entity(name = "Child")
+	public static class Child {
+
+		@Id
+		@GeneratedValue
+		private int id;
+
+		@ManyToOne
+		private Parent parent;
+
+		public int getId() {
+			return id;
+		}
+
+		public void setId(int id) {
+			this.id = id;
+		}
+
+		public Parent getParent() {
+			return parent;
+		}
+
+		public void setParent(Parent parent) {
+			this.parent = parent;
+		}
+	}
+
+	@Entity(name = "ParentCascade")
+	public static class ParentCascade {
+
+		@Id
+		@GeneratedValue
+		private Integer id;
+
+		@OneToMany(mappedBy = "parent", cascade = { CascadeType.ALL })
+		private List<ChildCascade> children = new ArrayList<ChildCascade>();
+
+		public Integer getId() {
+			return id;
+		}
+
+		public List<ChildCascade> getChildren() {
+			return children;
+		}
+
+		public void setChildren(List<ChildCascade> children) {
+			this.children = children;
+		}
+	}
+
+	@Entity(name = "ChildCascade")
+	public static class ChildCascade {
+
+		@Id
+		@GeneratedValue
+		private Integer id;
+
+		@ManyToOne
+		private ParentCascade parent;
+
+		public Integer getId() {
+			return id;
+		}
+
+		public ParentCascade getParent() {
+			return parent;
+		}
+
+		public void setParent(ParentCascade parent) {
+			this.parent = parent;
+		}
+	}
+}