feat(batch15): complete group 6 msgblock/consumerfilestore

dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ImplBacklog/ConcurrencyTests1.Impltests.cs

@@ -175,6 +175,59 @@ public sealed partial class ConcurrencyTests1
         }
     }
 
+    [Fact]
+    public void NoRaceJetStreamConsumerDeleteWithFlushPending_ShouldSucceed()
+    {
+        WithStore((fs, _) =>
+        {
+            const int consumerCount = 100;
+            var errors = new ConcurrentQueue<Exception>();
+            var ts = DateTimeOffset.UtcNow.ToUnixTimeSeconds() * 1_000_000_000L;
+            var workers = new List<Task>(consumerCount);
+
+            for (var i = 0; i < consumerCount; i++)
+            {
+                var consumer = fs.ConsumerStore(
+                    $"flush-del-{i}",
+                    DateTime.UtcNow,
+                    new ConsumerConfig { AckPolicy = AckPolicy.AckExplicit });
+
+                workers.Add(Task.Run(() =>
+                {
+                    var updater = Task.Run(() =>
+                    {
+                        for (ulong n = 1; n <= 50; n++)
+                        {
+                            try
+                            {
+                                consumer.UpdateDelivered(n, n, 1, ts + (long)n);
+                            }
+                            catch (Exception ex) when (ReferenceEquals(ex, StoreErrors.ErrStoreClosed))
+                            {
+                                break;
+                            }
+                        }
+                    });
+
+                    Thread.Sleep(1);
+
+                    try
+                    {
+                        consumer.Delete();
+                        updater.Wait();
+                    }
+                    catch (Exception ex)
+                    {
+                        errors.Enqueue(ex);
+                    }
+                }));
+            }
+
+            Task.WaitAll(workers.ToArray());
+            errors.ShouldBeEmpty();
+        });
+    }
+
     [Fact] // T:2441
     public void NoRaceJetStreamFileStoreLargeKVAccessTiming_ShouldSucceed()
     {