tests: editor WaitIdle also drains the thumbnail queue

Author: xen2

sources/editor/Stride.Core.Assets.Editor/Services/IThumbnailService.cs

@@ -33,6 +33,11 @@ public interface IThumbnailService : IDisposable
         /// <returns><c>True</c> if the asset type has static thumbnails, <c>False</c> otherwise.</returns>
         bool HasStaticThumbnail(Type assetType);
 
+        /// <summary>
+        /// Gets the number of thumbnails currently queued for compilation.
+        /// </summary>
+        int PendingThumbnailCount { get; }
+
         /// <summary>
         /// Raised when a thumbnail is successfully compiled.
         /// </summary>

sources/editor/Stride.Editor/Thumbnails/GameStudioThumbnailService.cs

@@ -125,6 +125,9 @@ public static byte[] HandleBrokenThumbnail()
 
         public event EventHandler<ThumbnailCompletedArgs> ThumbnailCompleted;
 
+        /// <inheritdoc/>
+        public int PendingThumbnailCount { get { lock (hashLock) return thumbnailQueueHash.Count; } }
+
         /// <inheritdoc/>
         public bool HasStaticThumbnail(Type assetType)
         {

sources/editor/Stride.GameStudio.AutoTesting/UITestHost.cs

@@ -248,6 +248,13 @@ public Task WaitForShaders() => WaitForQueueDrained("shader-compile", () =>
             return session?.ServiceProvider.TryGet<GameStudioBuilderService>()?.PendingShaderCompilationCount ?? 0;
         });
 
+        // Thumbnails build on a background queue; panel captures show blank tiles unless it is drained
+        public Task WaitForThumbnails() => WaitForQueueDrained("thumbnails", () =>
+        {
+            var session = TryGetSession();
+            return session?.ServiceProvider.TryGet<Stride.Core.Assets.Editor.Services.IThumbnailService>()?.PendingThumbnailCount ?? 0;
+        });
+
         public Task WaitDispatcherIdle()
         {
             var tcs = new TaskCompletionSource();
@@ -265,6 +272,7 @@ public async Task WaitIdle()
         {
             await WaitForAssetBuild();
             await WaitForShaders();
+            await WaitForThumbnails();
             await WaitDispatcherIdle();
             await WaitFrames(1);
             await WaitForRendering();