clear dispatcher queue at the end of tests.

tests/Avalonia.RenderTests/TestBase.cs

@@ -31,7 +31,7 @@ namespace Avalonia.Skia.RenderTests
 namespace Avalonia.Direct2D1.RenderTests
 #endif
 {
-    public class TestBase
+    public class TestBase : IDisposable
     {
 #if AVALONIA_SKIA
         private static string s_fontUri = "resm:Avalonia.Skia.RenderTests.Assets?assembly=Avalonia.Skia.RenderTests#Noto Mono";
@@ -282,5 +282,10 @@ namespace Avalonia.Direct2D1.RenderTests
                 });
             }
         }
+
+        public void Dispose()
+        {
+            Dispatcher.UIThread.RunJobs();
+        }
     }
 }

tests/Avalonia.UnitTests/TestWithServicesBase.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using Avalonia.Threading;
 
 namespace Avalonia.UnitTests
 {
@@ -17,6 +18,7 @@ namespace Avalonia.UnitTests
 
         public void Dispose()
         {
+            Dispatcher.UIThread.RunJobs();
             _scope.Dispose();
         }
     }

tests/Avalonia.UnitTests/UnitTestApplication.cs

@@ -46,6 +46,7 @@ namespace Avalonia.UnitTests
             Dispatcher.UIThread.UpdateServices();
             return Disposable.Create(() =>
             {
+                Dispatcher.UIThread.RunJobs();
                 scope.Dispose();
                 Dispatcher.UIThread.UpdateServices();
             });