fix: run markup updates in users sync context

Author: egil

CHANGELOG.md

@@ -6,6 +6,12 @@ All notable changes to **bUnit** will be documented in this file. The project ad
 
 ## [Unreleased]
 
+
+### Changed 
+
+- Changed test renderer such that updates to rendered components markup happen in the same synchronization context as the test framework is using (if any), if any, to avoid memory race conditions. By [@egil](https://github.com/egil).
+- Changed default "WaitFor" timeout to 10 seconds. By [@egil](https://github.com/egil).
+
 ## [1.18.4] - 2023-02-26
 
 ### Fixed

src/bunit.core/Rendering/TestRenderer.cs

@@ -8,6 +8,7 @@ namespace Bunit.Rendering;
 /// </summary>
 public class TestRenderer : Renderer, ITestRenderer
 {
+	private readonly SynchronizationContext? usersSyncContext = SynchronizationContext.Current;
 	private readonly Dictionary<int, IRenderedFragmentBase> renderedComponents = new();
 	private readonly List<RootComponent> rootComponents = new();
 	private readonly ILogger<TestRenderer> logger;
@@ -105,7 +106,6 @@ public Task DispatchEventAsync(
 		}
 
 		AssertNoUnhandledExceptions();
-
 		return result;
 	}
 
@@ -124,7 +124,6 @@ public IReadOnlyList<IRenderedComponentBase<TComponent>> FindComponents<TCompone
 		where TComponent : IComponent
 		=> FindComponents<TComponent>(parentComponent, int.MaxValue);
 
-
 	/// <inheritdoc />
 	public void DisposeComponents()
 	{
@@ -154,10 +153,38 @@ public void DisposeComponents()
 	/// <inheritdoc/>
 	protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
 	{
-		logger.LogNewRenderBatchReceived();
+		if (usersSyncContext is not null && usersSyncContext != SynchronizationContext.Current)
+		{
+			// The users' sync context, typically one established by
+			// xUnit or another testing framework is used to update any
+			// rendered fragments/dom trees and trigger WaitForX handlers.
+			// This ensures that changes to DOM observed inside a WaitForX handler
+			// will also be visible outside a WaitForX handler, since
+			// they will be running in the same sync context. The theory is that 
+			// this should mitigate the issues where Blazor's dispatcher/thread is used 
+			// to verify an assertion inside a WaitForX handler, and another thread is 
+			// used again to access the DOM/repeat the assertion, where the change
+			// may not be visible yet (another theory about why that may happen is different 
+			// CPU cache updates not happening immediately).
+			//
+			// There is no guarantee a caller/test framework has set a sync context.
+			usersSyncContext.Send(static (state) =>
+			{
+				var (renderBatch, renderer) = ((RenderBatch, TestRenderer))state!;
+				renderer.UpdateDisplay(renderBatch);
+			}, (renderBatch, this));
+		}
+		else
+		{
+			UpdateDisplay(renderBatch);
+		}
 
-		RenderCount++;
+		return Task.CompletedTask;
+	}
 
+	private void UpdateDisplay(in RenderBatch renderBatch)
+	{
+		RenderCount++;
 		var renderEvent = new RenderEvent(renderBatch, new RenderTreeFrameDictionary());
 
 		// removes disposed components
@@ -177,12 +204,12 @@ protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
 		// notify each rendered component about the render
 		foreach (var (key, rc) in renderedComponents.ToArray())
 		{
-			logger.LogComponentRendered(rc.ComponentId);
-
 			LoadRenderTreeFrames(rc.ComponentId, renderEvent.Frames);
 
 			rc.OnRender(renderEvent);
 
+			logger.LogComponentRendered(rc.ComponentId);
+
 			// RC can replace the instance of the component it is bound
 			// to while processing the update event.
 			if (key != rc.ComponentId)
@@ -191,10 +218,6 @@ protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
 				renderedComponents.Add(rc.ComponentId, rc);
 			}
 		}
-
-		logger.LogChangedComponentsMarkupUpdated();
-
-		return Task.CompletedTask;
 	}
 
 	/// <inheritdoc/>
@@ -255,45 +278,37 @@ private IReadOnlyList<IRenderedComponentBase<TComponent>> FindComponents<TCompon
 		if (parentComponent is null)
 			throw new ArgumentNullException(nameof(parentComponent));
 
-		// Ensure FindComponents runs on the same thread as the renderer,
-		// and that the renderer does not perform any renders while
-		// FindComponents is traversing the current render tree.
-		// Without this, the render tree could change while FindComponentsInternal
-		// is traversing down the render tree, with indeterministic as a results.
-		return Dispatcher.InvokeAsync(() =>
-		{
-			var result = new List<IRenderedComponentBase<TComponent>>();
-			var framesCollection = new RenderTreeFrameDictionary();
+		var result = new List<IRenderedComponentBase<TComponent>>();
+		var framesCollection = new RenderTreeFrameDictionary();
 
-			FindComponentsInRenderTree(parentComponent.ComponentId);
+		FindComponentsInRenderTree(parentComponent.ComponentId);
 
-			return result;
+		return result;
 
-			void FindComponentsInRenderTree(int componentId)
-			{
-				var frames = GetOrLoadRenderTreeFrame(framesCollection, componentId);
+		void FindComponentsInRenderTree(int componentId)
+		{
+			var frames = GetOrLoadRenderTreeFrame(framesCollection, componentId);
 
-				for (var i = 0; i < frames.Count; i++)
+			for (var i = 0; i < frames.Count; i++)
+			{
+				ref var frame = ref frames.Array[i];
+				if (frame.FrameType == RenderTreeFrameType.Component)
 				{
-					ref var frame = ref frames.Array[i];
-					if (frame.FrameType == RenderTreeFrameType.Component)
+					if (frame.Component is TComponent component)
 					{
-						if (frame.Component is TComponent component)
-						{
-							result.Add(GetOrCreateRenderedComponent(framesCollection, frame.ComponentId, component));
-
-							if (result.Count == resultLimit)
-								return;
-						}
-
-						FindComponentsInRenderTree(frame.ComponentId);
+						result.Add(GetOrCreateRenderedComponent(framesCollection, frame.ComponentId, component));
 
 						if (result.Count == resultLimit)
 							return;
 					}
+
+					FindComponentsInRenderTree(frame.ComponentId);
+
+					if (result.Count == resultLimit)
+						return;
 				}
 			}
-		}).GetAwaiter().GetResult();
+		}
 	}
 
 	IRenderedComponentBase<TComponent> GetOrCreateRenderedComponent<TComponent>(RenderTreeFrameDictionary framesCollection, int componentId, TComponent component)