fix: read the wrapped element once so a concurrent re-render cannot return null

CHANGELOG.md

@@ -6,6 +6,10 @@ All notable changes to **bUnit** will be documented in this file. The project ad
 
 ## [Unreleased]
 
+### Fixed
+
+- An element returned by `Find()` could be `null` for a moment when the component re-rendered on another thread, so using it threw a `NullReferenceException`, for example from `GetBunitContext` in `ClickAsync`. Reported and fixed by [@psu-prog](https://github.com/psu-prog).
+
 ## [2.11.3] - 2026-09-13
 
 ### Fixed

src/bunit.generators.internal/Web.AngleSharp/WrapperBase.cs

@@ -26,10 +26,8 @@ public TElement WrappedElement
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		get
 		{
-			if (element is null)
-				element = elementFactory.GetElement<TElement>();
-
-			return element;
+			// Read the field once: a re-render on another thread can reset it to null between two reads.
+			return element ??= elementFactory.GetElement<TElement>();
 		}
 	}
 

tests/bunit.generators.tests/Web.AngleSharp/WrapperElementsGeneratorTest.Generator#WrapperBase.g.verified.cs

@@ -27,10 +27,8 @@ public TElement WrappedElement
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		get
 		{
-			if (element is null)
-				element = elementFactory.GetElement<TElement>();
-
-			return element;
+			// Read the field once: a re-render on another thread can reset it to null between two reads.
+			return element ??= elementFactory.GetElement<TElement>();
 		}
 	}
 

tests/bunit.tests/Extensions/RefreshingWrappedElementTest.cs

@@ -76,6 +76,30 @@ public void Test031()
 		Should.Throw<ElementRemovedFromDomException>(() => btn.TextContent);
 	}
 
+	[Fact(DisplayName = "Found element is never null while the component re-renders on another thread")]
+	public async Task Test040()
+	{
+		var cut = Render<Counter>();
+		var elm = cut.Find("span");
+		using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(1));
+		var renders = Task.Run(async () =>
+		{
+			while (!cts.IsCancellationRequested)
+				await cut.InvokeAsync(cut.Instance.Increment);
+		});
+
+		try
+		{
+			while (!cts.IsCancellationRequested)
+				_ = elm.TextContent;
+		}
+		finally
+		{
+			await cts.CancelAsync();
+			await renders;
+		}
+	}
+
 	private sealed class Markup : ComponentBase
 	{
 		[Parameter] public string Base { get; set; } = string.Empty;
@@ -89,4 +113,22 @@ protected override void BuildRenderTree(RenderTreeBuilder builder)
 				builder.AddMarkupContent(1, Optional);
 		}
 	}
+
+	private sealed class Counter : ComponentBase
+	{
+		private int count;
+
+		public void Increment()
+		{
+			count++;
+			StateHasChanged();
+		}
+
+		protected override void BuildRenderTree(RenderTreeBuilder builder)
+		{
+			builder.OpenElement(0, "span");
+			builder.AddContent(1, count);
+			builder.CloseElement();
+		}
+	}
 }