diff --git a/src/core/Akka.TestKit.Tests/TestKitSpec.cs b/src/core/Akka.TestKit.Tests/TestKitSpec.cs
new file mode 100644
index 00000000000..5071af9d7e4
--- /dev/null
+++ b/src/core/Akka.TestKit.Tests/TestKitSpec.cs
@@ -0,0 +1,59 @@
+// -----------------------------------------------------------------------
+//
+// Copyright (C) 2009-2022 Lightbend Inc.
+// Copyright (C) 2013-2022 .NET Foundation
+//
+// -----------------------------------------------------------------------
+
+using Akka.Actor;
+using Akka.Actor.Dsl;
+using Akka.Configuration;
+using Xunit;
+using Xunit.Abstractions;
+using FluentAssertions;
+using static FluentAssertions.FluentActions;
+
+namespace Akka.TestKit.Tests
+{
+ public class TestKitSpec
+ {
+ private readonly ITestOutputHelper _output;
+
+ public TestKitSpec(ITestOutputHelper output)
+ {
+ _output = output;
+ }
+
+ [Fact(DisplayName = "TestKit should accept arbitrary ActorSystem")]
+ public void TestKitBaseTest()
+ {
+ using (var sys = ActorSystem.Create(nameof(TestKitSpec)))
+ {
+ var testkit = new TestKit.Xunit2.TestKit(sys, _output);
+ var echoActor = testkit.Sys.ActorOf(c => c.ReceiveAny((m, ctx) => testkit.TestActor.Tell(m)));
+ Invoking(() =>
+ {
+ echoActor.Tell("message");
+ var message = testkit.ExpectMsg();
+ message.Should().Be("message");
+ }).Should().NotThrow();
+ }
+ }
+
+ [Fact(DisplayName = "TestKit should accept ActorSystem with TestKit.DefaultConfig")]
+ public void TestKitConfigTest()
+ {
+ using (var sys = ActorSystem.Create(nameof(TestKitSpec), TestKit.Xunit2.TestKit.DefaultConfig))
+ {
+ var testkit = new TestKit.Xunit2.TestKit(sys, _output);
+ var echoActor = testkit.Sys.ActorOf(c => c.ReceiveAny((m, ctx) => testkit.TestActor.Tell(m)));
+ Invoking(() =>
+ {
+ echoActor.Tell("message");
+ var message = testkit.ExpectMsg();
+ message.Should().Be("message");
+ }).Should().NotThrow();
+ }
+ }
+ }
+}
\ No newline at end of file
diff --git a/src/core/Akka.TestKit/TestKitBase.cs b/src/core/Akka.TestKit/TestKitBase.cs
index 0dd2786b423..49f1c86410d 100644
--- a/src/core/Akka.TestKit/TestKitBase.cs
+++ b/src/core/Akka.TestKit/TestKitBase.cs
@@ -147,6 +147,10 @@ protected virtual void InitializeTest(ActorSystem system, ActorSystemSetup confi
}
system = ActorSystem.Create(actorSystemName ?? "test", config.WithSetup(newBootstrap));
}
+ else
+ {
+ system.Settings.InjectTopLevelFallback(_defaultConfig);
+ }
_testState.System = system;