fix: resolve implicit-sender leak under xUnit v3 parallel execution

Directory.Build.props

@@ -31,7 +31,7 @@
     <CoverletVersion>6.0.3</CoverletVersion>
     <XunitRunneVisualstudio>3.1.5</XunitRunneVisualstudio>
     <Xunit3RunneVisualstudio>3.1.5</Xunit3RunneVisualstudio>
-    <AkkaVersion>1.5.67</AkkaVersion>
+    <AkkaVersion>1.5.68</AkkaVersion>
     <MicrosoftExtensionsVersion>[9.0.0,)</MicrosoftExtensionsVersion>
     <SystemTextJsonVersion>[9.0.0,)</SystemTextJsonVersion>
   </PropertyGroup>

src/Akka.Hosting.API.Tests/verify/CoreApiSpec.ApproveTestKit.verified.txt

@@ -43,6 +43,7 @@ namespace Akka.Hosting.TestKit
         public System.Threading.Tasks.Task WithSnapshotSave(System.Func<Akka.Persistence.TestKit.SnapshotStoreSaveBehavior, System.Threading.Tasks.Task> behaviorSelector, System.Action execution) { }
         public System.Threading.Tasks.Task WithSnapshotSave(System.Func<Akka.Persistence.TestKit.SnapshotStoreSaveBehavior, System.Threading.Tasks.Task> behaviorSelector, System.Func<System.Threading.Tasks.Task> execution) { }
     }
+    [Akka.TestKit.Xunit.Attributes.AkkaCleanAmbientContext]
     public abstract class TestKit : Akka.TestKit.TestKitBase, System.IAsyncDisposable, Xunit.IAsyncLifetime
     {
         protected TestKit(string? actorSystemName = null, Xunit.ITestOutputHelper? output = null, System.TimeSpan? startupTimeout = default, Microsoft.Extensions.Logging.LogLevel logLevel = 2) { }

src/Akka.Hosting.TestKit.Tests/ParallelAmbientContextSpec.cs

@@ -0,0 +1,83 @@
+// -----------------------------------------------------------------------
+//  <copyright file="ParallelAmbientContextSpec.cs" company="Akka.NET Project">
+//      Copyright (C) 2013-2022 .NET Foundation <https://github.com/akkadotnet/akka.net>
+//  </copyright>
+// -----------------------------------------------------------------------
+
+using System;
+using System.Threading.Tasks;
+using Akka.Actor;
+using Akka.Actor.Internal;
+using Akka.TestKit;
+using Xunit;
+
+namespace Akka.Hosting.TestKit.Tests;
+
+public abstract class ParallelAmbientContextSpecBase : TestKit
+{
+    protected override void ConfigureAkka(AkkaConfigurationBuilder builder, IServiceProvider provider)
+    {
+    }
+
+    [Fact]
+    public async Task Implicit_sender_should_resolve_to_own_TestActor()
+    {
+        TestActor.Tell("ping");
+        await ExpectMsgAsync<string>(
+            "ping",
+            TimeSpan.FromSeconds(5),
+            cancellationToken: TestContext.Current.CancellationToken);
+        Assert.Equal(TestActor, LastSender);
+
+        await Task.Yield();
+        TestActor.Tell("ping-after-yield");
+        await ExpectMsgAsync<string>(
+            "ping-after-yield",
+            TimeSpan.FromSeconds(5),
+            cancellationToken: TestContext.Current.CancellationToken);
+        Assert.Equal(TestActor, LastSender);
+    }
+}
+
+public class ParallelAmbientContextSpec01 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec02 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec03 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec04 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec05 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec06 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec07 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec08 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec09 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec10 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec11 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec12 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec13 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec14 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec15 : ParallelAmbientContextSpecBase { }
+public class ParallelAmbientContextSpec16 : ParallelAmbientContextSpecBase { }
+
+public abstract class ParallelNoImplicitSenderSpecBase : TestKit, INoImplicitSender
+{
+    protected override void ConfigureAkka(AkkaConfigurationBuilder builder, IServiceProvider provider)
+    {
+    }
+
+    [Fact]
+    public async Task Current_should_be_null_both_pre_and_post_await()
+    {
+        Assert.Null(InternalCurrentActorCellKeeper.Current);
+        await Task.Yield();
+        Assert.Null(InternalCurrentActorCellKeeper.Current);
+        await Task.Yield();
+        Assert.Null(InternalCurrentActorCellKeeper.Current);
+    }
+}
+
+public class ParallelNoImplicitSenderSpec01 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec02 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec03 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec04 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec05 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec06 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec07 : ParallelNoImplicitSenderSpecBase { }
+public class ParallelNoImplicitSenderSpec08 : ParallelNoImplicitSenderSpecBase { }

src/Akka.Hosting.TestKit.Tests/Properties/AssemblyInfo.cs

@@ -32,4 +32,4 @@
 // by using the '*' as shown below:
 // [assembly: AssemblyVersion("1.0.*")]
 
-[assembly: CollectionBehavior(CollectionBehavior.CollectionPerAssembly, DisableTestParallelization = true)]
+[assembly: CollectionBehavior(CollectionBehavior.CollectionPerClass)]

src/Akka.Hosting.TestKit.Tests/xunit.runner.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://xunit.github.io/schema/current/xunit.runner.schema.json",
   "longRunningTestSeconds": 60,
-  "parallelizeAssembly": false,
-  "parallelizeTestCollections": false
+  "parallelizeAssembly": true,
+  "parallelizeTestCollections": true
 }

src/Akka.Hosting.TestKit/TestKit.Shared.cs

@@ -54,7 +54,7 @@ public IHost Host
         /// </summary>
         private void EnsureImplicitSender()
         {
-            if (this is not INoImplicitSender && TestActor != null)
+            if (this is not INoImplicitSender && InternalCurrentActorCellKeeper.Current == null && TestActor != null)
                 InternalCurrentActorCellKeeper.Current = (ActorCell)((ActorRefWithCell)TestActor).Underlying;
         }
 
@@ -192,12 +192,6 @@ private async Task InitializeAsyncCore()
             // TestActor initialization and registration now happens in AddStartup
             // before user actors are created, preventing race conditions
 
-            // ALWAYS set the implicit sender context on the current thread after initialization
-            // This ensures it's available on the thread where tests will run
-            // This is critical for tests using DI-created actors
-            if (this is not INoImplicitSender && TestActor != null)
-                InternalCurrentActorCellKeeper.Current = (ActorCell)((ActorRefWithCell)TestActor).Underlying;
-
             await BeforeTestStart();
         }
 
@@ -221,11 +215,6 @@ protected sealed override void InitializeTest(ActorSystem system, ActorSystemSet
 
         protected virtual Task BeforeTestStart()
         {
-            // Ensure the implicit sender is set on the current thread before each test
-            // This is critical because tests may run on different threads than initialization
-            if (this is not INoImplicitSender)
-                InternalCurrentActorCellKeeper.Current = (ActorCell)((ActorRefWithCell)TestActor).Underlying;
-
             return Task.CompletedTask;
         }
 

src/Akka.Hosting.TestKit/TestKit.cs

@@ -7,10 +7,12 @@
 using System;
 using System.Threading.Tasks;
 using Akka.Annotations;
+using Akka.TestKit.Xunit.Attributes;
 using Xunit;
 
 namespace Akka.Hosting.TestKit
 {
+    [AkkaCleanAmbientContext]
     public abstract partial class TestKit : IAsyncLifetime, IAsyncDisposable
     {
         [InternalApi]