Update ActionDebouncer.cs to support tests with no Sync context

src/DynamoCoreWpf/Utilities/ActionDebouncer.cs

@@ -26,7 +26,7 @@ public void Cancel()
 
         /// <summary>
         /// Delays the "action" for a "timeout" number of milliseconds
-        /// The input Action will run on same syncronization context as the Debounce method call.
+        /// The input Action will run on same syncronization context as the Debounce method call (or the thread pool if a sync context does not exist, ex. in non UI tests).
         /// </summary>
         /// <param name="timeout">Number of milliseconds to wait</param>
         /// <param name="action">The action to execute after the timeout runs out.</param>
@@ -36,6 +36,25 @@ public void Debounce(int timeout, Action action)
             Cancel();
             cts = new CancellationTokenSource();
 
+            // The TaskScheduler.FromCurrentSynchronizationContext() exists only if there is a valid SyncronizationContex.
+            // Calling this method from a non UI thread could have a null SyncronizationContex.Current,
+            // so in that case we use the default TaskScheduler which uses the thread pool.
+            TaskScheduler taskScheduler = null;
+            if (SynchronizationContext.Current != null)
+            {// This should always be the case in UI threads.
+                taskScheduler = TaskScheduler.FromCurrentSynchronizationContext();
+            }
+            else
+            {
+                // This might happen when running tests in non UI threads.
+                // But if we are in a UI thread, then log this as a potential error.
+                if (System.Windows.Application.Current?.Dispatcher?.Thread == Thread.CurrentThread)
+                {// UI thread.
+                    logger?.LogError("The UI thread does not seem to have a SyncronizationContext.");
+                }
+                taskScheduler = TaskScheduler.Default;
+            }
+
             Task.Delay(timeout, cts.Token).ContinueWith((t) =>
             {
                 try
@@ -50,7 +69,7 @@ public void Debounce(int timeout, Action action)
                     logger?.Log("Failed to run debounce action with the following error:");
                     logger?.Log(ex.ToString());
                 }
-            }, TaskScheduler.FromCurrentSynchronizationContext());
+            }, taskScheduler);
         }
 
         public void Dispose()

test/DynamoCoreWpfTests/DynamoTestUIBase.cs

@@ -59,7 +59,7 @@ private void PrettyPrint(object obj)
             Console.WriteLine("}");
         }
 
-        internal void SetupStartupDiagnostics()
+        internal void StartupDiagnostics()
         {
             System.Console.WriteLine($"PID {Process.GetCurrentProcess().Id} Start test: {TestContext.CurrentContext.Test.Name}");
             TestUtilities.WebView2Tag = TestContext.CurrentContext.Test.Name;
@@ -69,16 +69,16 @@ internal void SetupStartupDiagnostics()
             Dispatcher.CurrentDispatcher.Hooks.OperationPosted += Hooks_OperationPosted;
         }
 
-        internal void SetupBeforeCleanupDiagnostics()
+        internal void BeforeCleanupDiagnostics()
         {
-            Dispatcher.CurrentDispatcher.Hooks.OperationPosted -= Hooks_OperationPosted;
             if (!SkipDispatcherFlush)
             {
                 DispatcherUtil.DoEventsLoop(() => DispatcherOpsCounter == 0);
             }
+            Dispatcher.CurrentDispatcher.Hooks.OperationPosted -= Hooks_OperationPosted;
         }
 
-        internal void SetupAfterCleanupDiagnostics()
+        internal void AfterCleanupDiagnostics()
         {
             TestUtilities.WebView2Tag = string.Empty;
             using (var currentProc = Process.GetCurrentProcess())
@@ -93,10 +93,10 @@ internal void SetupAfterCleanupDiagnostics()
             }
         }
 
-        internal void SetupCleanupDiagnostics()
+        internal void CleanupDiagnostics()
         {
-            SetupBeforeCleanupDiagnostics();
-            SetupAfterCleanupDiagnostics();
+            BeforeCleanupDiagnostics();
+            AfterCleanupDiagnostics();
         }
     }
 
@@ -132,7 +132,7 @@ protected string ExecutingDirectory
         [SetUp]
         public virtual void Start()
         {
-            testDiagnostics.SetupStartupDiagnostics();
+            testDiagnostics.StartupDiagnostics();
             var assemblyPath = Assembly.GetExecutingAssembly().Location;
             preloader = new Preloader(Path.GetDirectoryName(assemblyPath));
             preloader.Preload();
@@ -229,7 +229,7 @@ public void Exit()
             {
                 Console.WriteLine(ex.StackTrace);
             }
-            testDiagnostics.SetupAfterCleanupDiagnostics();
+            testDiagnostics.AfterCleanupDiagnostics();
         }
 
         protected virtual void GetLibrariesToPreload(List<string> libraries)

test/DynamoCoreWpfTests/RecordedTests.cs

@@ -54,7 +54,7 @@ public class RecordedUnitTestBase : DynamoViewModelUnitTest
 
         public override void Setup()
         {
-            testDiagnostics.SetupStartupDiagnostics();
+            testDiagnostics.StartupDiagnostics();
 
             base.Setup();
             // Fixed seed randomizer for predictability.
@@ -63,10 +63,10 @@ public override void Setup()
 
         public override void Cleanup()
         {
-            testDiagnostics.SetupBeforeCleanupDiagnostics();
+            testDiagnostics.BeforeCleanupDiagnostics();
             commandCallback = null;
             base.Cleanup();
-            testDiagnostics.SetupAfterCleanupDiagnostics();
+            testDiagnostics.AfterCleanupDiagnostics();
         }
 
         #endregion