fix: captured error message from event dispatcher in renderer (related to #399)

Author: egil

CHANGELOG.md

@@ -38,18 +38,22 @@ List of fixes in this release.
 
 - Fixed issue where a registered fall-back service provider was not made available to resolve service dependencies of components under test. Thanks to [@dady8889](https://github.com/dady8889) for the reporting the issue.
 
-- Fixed handling of escaped uri's in FakeNavigationManager. By [@linkdotnet](https://github.com/linkdotnet) in [#460](https://github.com/bUnit-dev/bUnit/pull/460)
+- Fixed handling of escaped uri's in FakeNavigationManager. By [@linkdotnet](https://github.com/linkdotnet) in [#460](https://github.com/bUnit-dev/bUnit/pull/460).
+
+- Captured error message from event dispatcher in renderer that would previously be hidden from the user. Related to issue [#399](https://github.com/bUnit-dev/bUnit/issues/399).
 
 ## [1.1.5] - 2021-04-30
 
 ### Added
 
 - All bUnit assemblies is now strong named signed.
+
 - Added .NET 6 (preview 3) as a target framework for bUnit, bUnit.core and bUnit.web.
 
 ### Changed
 
 - Changed bunit.template such that created projects only reference the bUnit package. Bumped other referenced packages to latest version.
+
 - Changed TestServiceProvider to validate scopes of registered services, such that it behaves like the service provider (default IoC container) in Blazor.
 
 ## [1.0.16]

src/bunit.core/Rendering/TestRenderer.cs

@@ -73,7 +73,27 @@ public IRenderedComponentBase<TComponent> RenderComponent<TComponent>(ComponentP
 
 			ResetUnhandledException();
 
-			var result = Dispatcher.InvokeAsync(() => base.DispatchEventAsync(eventHandlerId, fieldInfo, eventArgs));
+			var result = Dispatcher.InvokeAsync(() =>
+			{
+				try
+				{
+					return base.DispatchEventAsync(eventHandlerId, fieldInfo, eventArgs);
+				}
+				catch (ArgumentException ex) when (string.Equals(ex.Message, $"There is no event handler associated with this event. EventId: '{eventHandlerId}'. (Parameter 'eventHandlerId')", StringComparison.Ordinal))
+				{
+					var betterExceptionMsg = new ArgumentException($"There is no event handler with ID '{eventHandlerId}' associated with the '{fieldInfo.FieldValue}' event " +
+						"in the current render tree. This can happen, for example, when using cut.FindAll(), and calling event trigger methods " +
+						"on the found elements after a re-render of the render tree. The workaround is to use re-issue the cut.FindAll() after " +
+						"each render of a component, this ensures you have the latest version of the render tree and DOM tree available in your test code.", ex);
+
+					return Task.FromException(betterExceptionMsg);
+				}
+			});
+
+			if(result.IsFaulted && result.Exception is not null)
+			{
+				HandleException(result.Exception);
+			}
 
 			AssertNoUnhandledExceptions();
 

tests/bunit.web.tests/EventDispatchExtensions/GeneralEventDispatchExtensionsTest.cs

@@ -174,5 +174,18 @@ public async Task Test114(
 			cut.Instance.ParentTriggerCount.ShouldBe(1);
 			cut.Instance.GrandParentTriggerCount.ShouldBe(1);
 		}
+
+
+		[Fact(DisplayName = "TriggerEventAsync throws when invoked with an unknown event handler ID")]
+		public void Test115()
+		{
+			var eventName = "onclick";
+			var cut = RenderComponent<Wrapper>(ps => ps.AddChildContent("<div />"));
+			var div = cut.Find("div");
+			div.SetAttribute(Htmlizer.ToBlazorAttribute(eventName), "42");
+
+			Should.Throw<ArgumentException>(() => div.TriggerEventAsync(eventName, EventArgs.Empty));
+		}
+
 	}
 }