Add graceful stop specs (#6103)

* added `GracefulStop` specs

* added one more use case

* fixing up some buggy `ActorLifeCycleSpec`s

src/core/Akka.Tests/Actor/ActorLifeCycleSpec.cs

@@ -213,31 +213,21 @@ public class Become
         }
         public class BecomeActor : UntypedActor
         {
-            private IActorRef testActor;
+            private readonly IActorRef _testActor;
             public BecomeActor(IActorRef testActor)
             {
-                this.testActor = testActor;
-            }
-
-            protected override void PreRestart(Exception cause, object message)
-            {
-                base.PreRestart(cause, message);
-            }
-
-            protected override void PostRestart(Exception cause)
-            {
-                base.PostRestart(cause);
+                _testActor = testActor;
             }
             protected override void OnReceive(object message)
             {
                 if (message is Become)
                 {
                     Context.Become(OnBecome);
-                    testActor.Tell("ok");
+                    _testActor.Tell("ok");
                 }
                 else
                 {
-                    testActor.Tell(42);
+                    _testActor.Tell(42);
                 }
             }
 
@@ -249,7 +239,7 @@ protected void OnBecome(object message)
                 }
                 else
                 {
-                    testActor.Tell(43);
+                    _testActor.Tell(43);
                 }
             }
         }
@@ -266,7 +256,12 @@ public async Task Clear_behavior_stack_upon_restart()
             a.Tell("hello");
             await ExpectMsgAsync(43);
 
-            await EventFilter.Exception<Exception>("buh").ExpectOneAsync(async () => a.Tell("fail"));
+            await EventFilter.Exception<Exception>("buh").ExpectOneAsync(async () =>
+            {
+                a.Tell("fail");
+                await Task.CompletedTask;
+            });
+
             a.Tell("hello");
             await ExpectMsgAsync(42);
         }

src/core/Akka.Tests/Actor/GracefulStopSpecs.cs

@@ -0,0 +1,71 @@
+//-----------------------------------------------------------------------
+// <copyright file="GracefulStopSpecs.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2022 Lightbend Inc. <http://www.lightbend.com>
+//     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.Dsl;
+using Akka.TestKit;
+using Akka.TestKit.TestActors;
+using Xunit;
+using FluentAssertions;
+
+namespace Akka.Tests.Actor
+{
+    public class GracefulStopSpecs : AkkaSpec
+    {
+        [Fact(DisplayName = "GracefulStop should terminate target actor on-time")]
+        public async Task GracefulStopShouldTerminateOnTime()
+        {
+            // arrange
+            var actor = Sys.ActorOf(BlackHoleActor.Props);
+            Watch(actor);
+
+            // act
+            var stopped = await actor.GracefulStop(TimeSpan.FromSeconds(3));
+            await ExpectTerminatedAsync(actor);
+
+            // assert
+            stopped.Should().BeTrue();
+        }
+
+        [Fact(DisplayName = "GracefulStop should return true for an already terminated actor")]
+        public async Task GracefulStopShouldReturnTrueForAlreadyDeadActor()
+        {
+            // arrange
+            var actor = Sys.ActorOf(BlackHoleActor.Props);
+            Watch(actor);
+
+            // act
+            Sys.Stop(actor);
+            await ExpectTerminatedAsync(actor);
+            var stopped = await actor.GracefulStop(TimeSpan.FromSeconds(3));
+
+            // assert
+            stopped.Should().BeTrue();
+        }
+
+        private class CustomShutdown{}
+
+        [Fact(DisplayName = "GracefulStop should return false if shutdown goes overtime", Skip = "GracefulStop currently throws a TaskCancellationException, which seems wrong")]
+        public async Task GracefulStopShouldThrowIfShutdownGoesOvertime()
+        {
+            // arrange
+            var actor = Sys.ActorOf(act => act.ReceiveAsync<CustomShutdown>(async (a, ctx) =>
+            {
+                await Task.Delay(200);
+                ctx.Stop(ctx.Self);
+            }));
+
+            // act
+            var stopped = await actor.GracefulStop(TimeSpan.FromMilliseconds(10), new CustomShutdown());
+
+            // assert
+            stopped.Should().BeFalse();
+        }
+    }
+}