Simplify InvalidGroupIdentifier test using UpdateGroupIdentifier API (#343)

* Initial plan

* Add unit test for invalid GroupIdentifierConfig.EntityProperty validation

Co-authored-by: Yvand <8788631+Yvand@users.noreply.github.com>

* Refactor: Move InvalidGroupIdentifier test to CustomizeConfigTests

Co-authored-by: Yvand <8788631+Yvand@users.noreply.github.com>

* Shorten assertion message in InvalidGroupIdentifier test

Co-authored-by: Yvand <8788631+Yvand@users.noreply.github.com>

* Simplify InvalidGroupIdentifier test using UpdateGroupIdentifier method

Co-authored-by: Yvand <8788631+Yvand@users.noreply.github.com>

* Update CustomizeConfigTests.cs

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Yvand <8788631+Yvand@users.noreply.github.com>
Co-authored-by: Yvan Duhamel <yvandev@outlook.fr>

Author: Copilot

Yvand.EntraCP.Tests/CustomizeConfigTests.cs

@@ -173,5 +173,20 @@ public void ModifyUserIdentifier()
             configUpdated = Settings.ClaimTypes.UpdateIdentifierForGuestUsers(backupIdentityCTConfig.DirectoryObjectPropertyForGuestUsers);
             Assert.That(configUpdated, Is.False, $"Update user identifier of Guest UserType with the same DirectoryObjectProperty should not change anything and return false");
         }
+
+        [Test]
+        public void InvalidGroupIdentifier()
+        {
+            if (Settings.ClaimTypes.GroupIdentifierConfig != null)
+            {
+                DirectoryObjectProperty backupGroupIdentifier = Settings.ClaimTypes.GroupIdentifierConfig.EntityProperty;
+                // Update GroupIdentifierConfig to use UserPrincipalName, which exists for User but not Group
+                Settings.ClaimTypes.UpdateGroupIdentifier(DirectoryObjectProperty.UserPrincipalName);
+
+                // ValidateConfiguration should throw InvalidOperationException because the group identifier property is invalid
+                Assert.Throws<InvalidOperationException>(() => UnitTestsHelper.PersistedConfiguration.ApplySettings(Settings, true), "ValidateConfiguration should throw when GroupIdentifierConfig.EntityProperty doesn't exist for Group");
+                Settings.ClaimTypes.UpdateGroupIdentifier(backupGroupIdentifier);
+            }
+        }
     }
 }