feat: Error when no setup is made for JS

Author: linkdotnet

src/bunit/JSInterop/InvocationHandlers/JSRuntimeInvocationHandlerBase{TResult}.cs

@@ -82,7 +82,14 @@ protected void SetResultBase(TResult result)
 	protected internal virtual Task<TResult> HandleAsync(JSRuntimeInvocation invocation)
 	{
 		Invocations.RegisterInvocation(invocation);
-		return completionSource.Task;
+
+		var task = completionSource.Task;
+		if (task is { IsCanceled: false, IsFaulted: false, IsCompletedSuccessfully: false })
+		{
+			throw new JSRuntimeInvocationNotSetException(invocation);
+		}
+
+		return task;
 	}
 
 	/// <summary>

src/bunit/JSInterop/JSRuntimeInvocationNotSetException.cs

@@ -0,0 +1,48 @@
+using System.Text;
+
+namespace Bunit;
+
+/// <summary>
+/// Exception used to indicate that an invocation was received by a JSRuntime invocation handler,
+/// but the handler was not configured with a result (via SetResult, SetVoidResult, SetCanceled, or SetException).
+/// This causes the invocation to hang indefinitely.
+/// </summary>
+public sealed class JSRuntimeInvocationNotSetException : Exception
+{
+	/// <summary>
+	/// Gets the invocation that was not handled with a result.
+	/// </summary>
+	public JSRuntimeInvocation Invocation { get; }
+
+	/// <summary>
+	/// Initializes a new instance of the <see cref="JSRuntimeInvocationNotSetException"/> class
+	/// with the provided <see cref="Invocation"/> attached.
+	/// </summary>
+	/// <param name="invocation">The invocation that was not provided with a result.</param>
+	public JSRuntimeInvocationNotSetException(JSRuntimeInvocation invocation)
+		: base(CreateErrorMessage(invocation))
+	{
+		Invocation = invocation;
+	}
+
+	[SuppressMessage("Minor Code Smell", "S6618:\"string.Create\" should be used instead of \"FormattableString\"", Justification = "string.Create not supported in all TFs")]
+	private static string CreateErrorMessage(JSRuntimeInvocation invocation)
+	{
+		var sb = new StringBuilder();
+		sb.AppendLine("bUnit's JSInterop invocation handler was setup to handle the call:");
+		sb.AppendLine();
+		sb.AppendLine($"    {invocation.InvocationMethodName}");
+		sb.AppendLine();
+		sb.AppendLine("However, the invocation handler was not configured to return a result,");
+		sb.AppendLine("causing the invocation to hang indefinitely.");
+		sb.AppendLine();
+		sb.AppendLine("To fix this, configure the handler to return a result using one of the following methods:");
+		sb.AppendLine();
+		sb.AppendLine("    handler.SetVoidResult();");
+		sb.AppendLine("    handler.SetResult(result);");
+		sb.AppendLine("    handler.SetCanceled();");
+		sb.AppendLine("    handler.SetException(new Exception(\"error message\"));");
+
+		return sb.ToString();
+	}
+}

tests/bunit.tests/JSInterop/BunitJSInteropTest.cs

@@ -686,4 +686,17 @@ public void Test308(string identifier, string arg0, string arg1, string arg2)
 				invocationMethodName: "InvokeUnmarshalled"));
 	}
 #endif
+
+	[Fact(DisplayName = "JSRuntime invocation throws exception immediately when handler is not configured with result")]
+	public void Test309()
+	{
+		var identifier = "testFunction";
+		var sut = CreateSut(JSRuntimeMode.Strict);
+		sut.Setup<int>(identifier);
+		
+		var exception = Should.Throw<JSRuntimeInvocationNotSetException>(
+			() => sut.JSRuntime.InvokeAsync<int>(identifier));
+		
+		exception.Invocation.Identifier.ShouldBe(identifier);
+	}
 }