test: Nested NetworkObjects in prefabs throws a warning [MTT-2976]

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -9,6 +9,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ## [Unreleased]
 
 ### Added
+- Added test to ensure a warning occurs when nesting NetworkObjects in a NetworkPrefab
 
 - Added `NetworkManager.RemoveNetworkPrefab(...)` to remove a prefab from the prefabs list (#1950)
 

com.unity.netcode.gameobjects/Runtime/Core/NetworkManager.cs

@@ -424,7 +424,7 @@ public Func<ConnectionApprovalRequest, ConnectionApprovalResponse> ConnectionApp
         internal static event Action OnSingletonReady;
 
 #if UNITY_EDITOR
-        private void OnValidate()
+        internal void OnValidate()
         {
             if (NetworkConfig == null)
             {

com.unity.netcode.gameobjects/Tests/Editor/NetworkManagerConfigurationTests.cs

@@ -1,6 +1,8 @@
 using NUnit.Framework;
 using UnityEngine;
 using Unity.Netcode.Editor;
+using UnityEditor.SceneManagement;
+using UnityEngine.SceneManagement;
 using UnityEngine.TestTools;
 
 namespace Unity.Netcode.EditorTests
@@ -78,5 +80,37 @@ public void NetworkObjectNotAllowed([Values] NetworkObjectPlacement networkObjec
             // Clean up
             Object.DestroyImmediate(gameObject);
         }
+
+        [Test]
+        public void NestedNetworkObjectPrefabCheck()
+        {
+            // Setup
+            var networkManagerObject = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager = networkManagerObject.AddComponent<NetworkManager>();
+            networkManager.NetworkConfig = new NetworkConfig();
+
+            var parent = new GameObject("Parent").AddComponent<NetworkObject>();
+            var child = new GameObject("Child").AddComponent<NetworkObject>();
+
+            // Set parent
+            child.transform.SetParent(parent.transform);
+
+            // Make it a prefab, warning only applies to prefabs
+            networkManager.AddNetworkPrefab(parent.gameObject);
+
+            // Mark scene as dirty to ensure OnValidate actually runs
+            EditorSceneManager.MarkSceneDirty(SceneManager.GetActiveScene());
+
+            // Force OnValidate
+            networkManager.OnValidate();
+
+            // Expect a warning
+            LogAssert.Expect(LogType.Warning, $"[Netcode] {NetworkManager.PrefabDebugHelper(networkManager.NetworkConfig.NetworkPrefabs[0])} has child {nameof(NetworkObject)}(s) but they will not be spawned across the network (unsupported {nameof(NetworkPrefab)} setup)");
+
+            // Clean up
+            Object.DestroyImmediate(networkManagerObject);
+            Object.DestroyImmediate(parent);
+
+        }
     }
 }