test(batch26): port cross-module websocket-dependent tests

dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ImplBacklog/ConcurrencyTests2.Impltests.cs

@@ -330,6 +330,64 @@ public sealed partial class ConcurrencyTests2
         }, cfg);
     }
 
+    [Fact] // T:2488
+    public void NoRaceJetStreamSnapshotsWithSlowAckDontSlowConsumer_ShouldSucceed()
+    {
+        var cfg = DefaultStreamConfig();
+        cfg.Subjects = ["snap.>"];
+
+        WithStore((fs, _) =>
+        {
+            var errors = new ConcurrentQueue<Exception>();
+            using var cts = new CancellationTokenSource();
+            var payload = "snapshot"u8.ToArray();
+            var ts = DateTimeOffset.UtcNow.ToUnixTimeSeconds() * 1_000_000_000L;
+            var consumer = fs.ConsumerStore("snap-consumer", DateTime.UtcNow, new ConsumerConfig { AckPolicy = AckPolicy.AckExplicit });
+
+            var slowAcker = Task.Run(async () =>
+            {
+                for (ulong i = 1; i <= 100; i++)
+                {
+                    try
+                    {
+                        consumer.UpdateDelivered(i, i, 1, ts + (long)i);
+                        await Task.Delay(2, cts.Token);
+                    }
+                    catch (OperationCanceledException)
+                    {
+                        break;
+                    }
+                    catch (Exception ex)
+                    {
+                        errors.Enqueue(ex);
+                        break;
+                    }
+                }
+            });
+
+            for (var i = 0; i < 100; i++)
+                fs.StoreMsg($"snap.{i % 5}", null, payload, 0);
+
+            var sw = Stopwatch.StartNew();
+            var (snapshot, err) = fs.Snapshot(TimeSpan.FromSeconds(2), includeConsumers: true, checkMsgs: true);
+            sw.Stop();
+
+            err.ShouldBeNull();
+            snapshot.ShouldNotBeNull();
+            snapshot!.State.Msgs.ShouldBeGreaterThan(0UL);
+            sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(2));
+
+            using (snapshot.Reader)
+            {
+            }
+
+            cts.Cancel();
+            Should.NotThrow(() => slowAcker.Wait(TimeSpan.FromSeconds(1)));
+            errors.ShouldBeEmpty();
+            consumer.Stop();
+        }, cfg);
+    }
+
     private static void WithStore(Action<JetStreamFileStore, string> action, StreamConfig? cfg = null)
     {
         var root = NewRoot();