m2m sort duplication test case

ebean-test/src/test/java/org/tests/m2m/TestM2MSortTest.java

@@ -0,0 +1,40 @@
+package org.tests.m2m;
+
+import io.ebean.DB;
+import io.ebean.xtest.BaseTestCase;
+import org.junit.jupiter.api.Test;
+import org.tests.model.basic.MRole;
+import org.tests.model.basic.MUser;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class TestM2MSortTest extends BaseTestCase {
+
+  @Test
+  public void test() {
+    // Create 2 roles r0 and r1
+    MRole r0 = new MRole("r0");
+    MRole r1 = new MRole("r1");
+
+    // Save r1 and r2
+    DB.save(r0);
+    DB.save(r1);
+
+    // Create new users
+    MUser u0 = new MUser("usr0");
+    u0.addRole(r0);
+    u0.addRole(r1);
+    MUser u1 = new MUser("usr1");
+    u1.addRole(r0);
+
+    // Save the users
+    DB.save(u0);
+    DB.save(u1);
+
+    var users = DB.find(MUser.class).orderBy("roles").findList();
+    assertThat(users).hasSize(2);
+  }
+}