diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/VirtualTags/VirtualTagHostActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/VirtualTags/VirtualTagHostActorTests.cs
index 76bc7396..9d6838a2 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/VirtualTags/VirtualTagHostActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/VirtualTags/VirtualTagHostActorTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using Akka.Actor;
 using Shouldly;
 using Xunit;
@@ -191,7 +192,8 @@ public sealed class VirtualTagHostActorTests : RuntimeActorTestBase
 
         // Wait for the history record to land (delivered on the same actor turn as the publish).
         AwaitAssert(() => writer.Calls.Count.ShouldBe(1));
-        var (path, value) = writer.Calls[0];
+        writer.Calls.TryPeek(out var captured).ShouldBeTrue();
+        var (path, value) = captured;
         path.ShouldBe("eq-1/speed-rpm");
         value.Value.ShouldBe(42.0);
         value.StatusCode.ShouldBe(0u); // OPC UA Good
@@ -213,11 +215,10 @@ public sealed class VirtualTagHostActorTests : RuntimeActorTestBase
 
         host.Tell(new VirtualTagActor.EvaluationResult("vt-1", 42.0, DateTime.UtcNow, CorrelationId.NewId()));
 
-        // The value is still published…
+        // The value is still published — and the publish completing means OnResult's turn is done,
+        // so the historian (which would have been called on the same turn) was never touched.
         publish.ExpectMsg<OpcUaPublishActor.AttributeValueUpdate>();
-        // …but the historian was never touched.
-        publish.ExpectNoMsg(TimeSpan.FromMilliseconds(200));
-        writer.Calls.ShouldBeEmpty();
+        writer.Calls.IsEmpty.ShouldBeTrue();
     }
 
     /// <summary>A plan with an explicit Expression + DependencyRefs (the H1b in-place-change case).</summary>
@@ -348,12 +349,14 @@ public sealed class VirtualTagHostActorTests : RuntimeActorTestBase
     /// assert the host historizes (or does not) and with what path + snapshot.</summary>
     private sealed class CapturingHistoryWriter : IHistoryWriter
     {
-        public readonly List<(string Path, DataValueSnapshot Value)> Calls = new();
+        // ConcurrentQueue: Record runs on the actor thread, the test asserts on the test thread —
+        // a plain List would be a cross-thread data race under load.
+        public readonly ConcurrentQueue<(string Path, DataValueSnapshot Value)> Calls = new();
 
         /// <summary>Captures the path + snapshot of a Record call.</summary>
         /// <param name="path">The virtual tag path.</param>
         /// <param name="value">The data value snapshot.</param>
-        public void Record(string path, DataValueSnapshot value) => Calls.Add((path, value));
+        public void Record(string path, DataValueSnapshot value) => Calls.Enqueue((path, value));
     }
 
     /// <summary>Deterministic no-op evaluator: keeps spawned children inert so tests drive the host's