Fixed tests

src/Avalonia.Base/Threading/DispatcherOperation.cs

@@ -105,9 +105,7 @@ public class DispatcherOperation
     {
         lock (Dispatcher.InstanceLock)
         {
-            if (Status == DispatcherOperationStatus.Pending)
-                return;
-            Dispatcher.Abort(this);
+            if (Status == DispatcherOperationStatus.Pending) Dispatcher.Abort(this);
         }
     }
 

src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs

@@ -184,6 +184,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
                 _cts?.Cancel();
                 _cts = null;
                 _isShuttingDown = false;
+                Dispatcher.UIThread.BeginInvokeShutdown(DispatcherPriority.Send);
             }
 
             return true;

tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Controls.Platform;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Threading;
@@ -13,17 +15,22 @@ namespace Avalonia.Controls.UnitTests
     
     public class DesktopStyleApplicationLifetimeTests
     {
-        IDispatcherImpl CreateDispatcherWithInstantMainLoop() => Mock.Of<IControlledDispatcherImpl>(x => x.CurrentThreadIsLoopThread == true);
-
-
+        IDispatcherImpl CreateDispatcherWithInstantMainLoop()
+        {
+            var mock = new Mock<IControlledDispatcherImpl>();
+            mock.Setup(x => x.RunLoop(It.IsAny<CancellationToken>()))
+                .Callback(() => Dispatcher.UIThread.ExitAllFrames());
+            mock.Setup(x => x.CurrentThreadIsLoopThread).Returns(true);
+            return mock.Object;
+        }
+        
         [Fact]
         public void Should_Set_ExitCode_After_Shutdown()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
+            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: new ManagedDispatcherImpl(null))))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())    
             {
-                lifetime.Shutdown(1337);
-
+                Dispatcher.UIThread.Post(() => lifetime.Shutdown(1337));
                 var exitCode = lifetime.Start(Array.Empty<string>());
 
                 Assert.Equal(1337, exitCode);
@@ -219,11 +226,14 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Should_Allow_Canceling_Shutdown_Via_ShutdownRequested_Event()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: new ManagedDispatcherImpl(null))))
             using (var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 var lifetimeEvents = new Mock<IPlatformLifetimeEventsImpl>();
                 AvaloniaLocator.CurrentMutable.Bind<IPlatformLifetimeEventsImpl>().ToConstant(lifetimeEvents.Object);
+                
+                // Force exit immediately
+                Dispatcher.UIThread.Post(Dispatcher.UIThread.ExitAllFrames);
                 lifetime.Start(Array.Empty<string>());
 
                 var window = new Window();
@@ -356,7 +366,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Shutdown_NotCancellable_By_Preventing_Window_Close()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 var hasExit = false;