test: add networkscenemanager additive scene loading tests

com.unity.netcode.gameobjects/Runtime/SceneManagement/NetworkSceneManager.cs

@@ -96,6 +96,12 @@ public class NetworkSceneManager
         /// </summary>
         private static bool s_IsSceneEventActive = false;
 
+        // TODO: Remove `m_IsRunningUnitTest` entirely after we switch to multi-process testing
+        // In MultiInstance tests, we cannot allow clients to load additional scenes as they're sharing the same scene space / Unity instance.
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+        private readonly bool m_IsRunningUnitTest = SceneManager.GetActiveScene().name.StartsWith("InitTestScene");
+#endif
+
         /// <summary>
         /// The delegate callback definition for scene event notifications
         /// For more details review over <see cref="SceneEvent"/> and <see cref="SceneEventData"/>
@@ -538,11 +544,21 @@ private void OnClientUnloadScene()
                     $"because the client scene handle {sceneHandle} was not found in ScenesLoaded!");
             }
             s_IsSceneEventActive = true;
-
-            var sceneUnload = SceneManager.UnloadSceneAsync(ScenesLoaded[sceneHandle]);
-
+            var sceneUnload = (AsyncOperation)null;
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+            if (m_IsRunningUnitTest)
+            {
+                sceneUnload = new AsyncOperation();
+            }
+            else
+            {
+                sceneUnload = SceneManager.UnloadSceneAsync(ScenesLoaded[sceneHandle]);
+                sceneUnload.completed += asyncOp2 => OnSceneUnloaded();
+            }
+#else
+            sceneUnload = SceneManager.UnloadSceneAsync(ScenesLoaded[sceneHandle]);
             sceneUnload.completed += asyncOp2 => OnSceneUnloaded();
-
+#endif
             ScenesLoaded.Remove(sceneHandle);
 
             // Remove our server to scene handle lookup
@@ -559,6 +575,12 @@ private void OnClientUnloadScene()
             });
 
 
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+            if (m_IsRunningUnitTest)
+            {
+                OnSceneUnloaded();
+            }
+#endif
         }
 
         /// <summary>
@@ -704,6 +726,33 @@ private void OnClientSceneLoadingEvent(Stream objectStream)
                 return;
             }
 
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+            if (m_IsRunningUnitTest)
+            {
+                // Send the loading message
+                OnSceneEvent?.Invoke(new SceneEvent()
+                {
+                    AsyncOperation = new AsyncOperation(),
+                    SceneEventType = SceneEventData.SceneEventType,
+                    LoadSceneMode = SceneEventData.LoadSceneMode,
+                    SceneName = sceneName,
+                    ClientId = m_NetworkManager.LocalClientId
+                });
+
+                // Unit tests must mirror the server's scenes loaded dictionary, otherwise this portion will fail
+                if (ScenesLoaded.ContainsKey(SceneEventData.SceneHandle))
+                {
+                    OnClientLoadedScene(ScenesLoaded[SceneEventData.SceneHandle]);
+                }
+                else
+                {
+                    throw new Exception($"Could not find the scene handle {SceneEventData.SceneHandle} for scene {GetSceneNameFromNetcodeSceneIndex(SceneEventData.SceneIndex)} " +
+                        $"during unit test.  Did you forget to register this in the unit test?");
+                }
+                return;
+            }
+#endif
+
             if (SceneEventData.LoadSceneMode == LoadSceneMode.Single)
             {
                 // Move ALL NetworkObjects to the temp scene
@@ -973,25 +1022,44 @@ private void OnClientBeginSync()
                 ScenePlacedObjects.Clear();
             }
 
+            var shouldPassThrough = false;
+            var sceneLoad = (AsyncOperation)null;
+
             // Check to see if the client already has loaded the scene to be loaded
-            if (sceneName != activeScene.name)
+            if (sceneName == activeScene.name)
             {
-                // If not, then load the scene
-                var sceneLoad = SceneManager.LoadSceneAsync(sceneName, loadSceneMode);
-
-                // Notify local client that a scene load has begun
-                OnSceneEvent?.Invoke(new SceneEvent()
-                {
-                    AsyncOperation = sceneLoad,
-                    SceneEventType = SceneEventData.SceneEventTypes.S2C_Load,
-                    LoadSceneMode = loadSceneMode,
-                    SceneName = sceneName,
-                    ClientId = m_NetworkManager.LocalClientId,
-                });
+                // If the client is already in the same scene, then pass through and
+                // don't try to reload it.
+                shouldPassThrough = true;
+            }
 
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+            if (m_IsRunningUnitTest)
+            {
+                // In unit tests, we don't allow clients to load additional scenes since
+                // MultiInstance unit tests share the same scene space.
+                shouldPassThrough = true;
+                sceneLoad = new AsyncOperation();
+            }
+#endif
+            if (!shouldPassThrough)
+            {
+                // If not, then load the scene
+                sceneLoad = SceneManager.LoadSceneAsync(sceneName, loadSceneMode);
                 sceneLoad.completed += asyncOp2 => ClientLoadedSynchronization(sceneIndex, sceneHandle);
             }
-            else
+
+            // Notify local client that a scene load has begun
+            OnSceneEvent?.Invoke(new SceneEvent()
+            {
+                AsyncOperation = sceneLoad,
+                SceneEventType = SceneEventData.SceneEventTypes.S2C_Load,
+                LoadSceneMode = loadSceneMode,
+                SceneName = sceneName,
+                ClientId = m_NetworkManager.LocalClientId,
+            });
+
+            if (shouldPassThrough)
             {
                 // If so, then pass through
                 ClientLoadedSynchronization(sceneIndex, sceneHandle);

testproject/Assets/Tests/Manual/Scripts/NetworkPrefabPool.cs

@@ -121,15 +121,18 @@ private void OnSceneEvent(SceneEvent sceneEvent)
         /// </summary>
         private void OnUnloadScene()
         {
-            if (IsServer)
+            if (NetworkObject != null && NetworkManager != null)
             {
-                StopCoroutine(SpawnObjects());
-            }
+                if (IsServer)
+                {
+                    StopCoroutine(SpawnObjects());
+                }
 
-            // De-register the custom prefab handler
-            DeregisterCustomPrefabHandler();
+                // De-register the custom prefab handler
+                DeregisterCustomPrefabHandler();
 
-            CleanNetworkObjects();
+                CleanNetworkObjects();
+            }
         }