HHH-15201 Add test for issue

hibernate-core/src/test/java/org/hibernate/orm/test/entitymode/map/compositeId/CompId.hbm.xml

@@ -0,0 +1,13 @@
+<!DOCTYPE hibernate-mapping PUBLIC
+        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
+        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
+
+<hibernate-mapping>
+    <class entity-name="CompId">
+        <composite-id>
+            <key-property name="id1" column="id1" length="32" type="string"/>
+            <key-property name="id2" column="id2" length="32" type="string"/>
+        </composite-id>
+        <property name="name" type="string"/>
+    </class>
+</hibernate-mapping>

hibernate-core/src/test/java/org/hibernate/orm/test/entitymode/map/compositeId/CompositeIdTest.java

@@ -0,0 +1,54 @@
+/*
+ * 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.orm.test.entitymode.map.compositeId;
+
+import java.util.HashMap;
+
+import org.hibernate.testing.TestForIssue;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+@DomainModel(
+		xmlMappings = "org/hibernate/orm/test/entitymode/map/compositeId/CompId.hbm.xml"
+)
+@SessionFactory
+@TestForIssue(jiraKey = "HHH-15201")
+public class CompositeIdTest {
+
+	@Test
+	public void testImplicitCompositeIdInDynamicMapMode(SessionFactoryScope scope) {
+		scope.inTransaction(
+				session -> {
+					HashMap<Object, Object> id = new HashMap<>();
+					id.put( "id1", "1" );
+					id.put( "id2", "2" );
+					id.put( "name", "Fab" );
+
+					session.save( "CompId", id );
+				}
+		);
+
+		scope.inTransaction(
+				session -> {
+					HashMap<Object, Object> id = new HashMap<>();
+					id.put( "id1", "1" );
+					id.put( "id2", "2" );
+					HashMap<Object, Object> compId = (HashMap<Object, Object>) session.get( "CompId", id );
+					assertNotNull( compId );
+					assertThat( compId.get( "id1" ), is( "1" ) );
+					assertThat( compId.get( "id2" ), is( "2" ) );
+					assertThat( compId.get( "name" ), is( "Fab" ) );
+				}
+		);
+	}
+}