Add unit test: should_wait_for_unsubscribe_to_complete_before_adding_new_subscriptions

src/Abc.Zebus.Tests/Core/BusTests.Subscribe.cs

@@ -1,4 +1,5 @@
-using System.Collections.Concurrent;
+using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -332,6 +333,41 @@ namespace Abc.Zebus.Tests.Core
                 _messageDispatcherMock.Verify(x => x.AddInvoker(It.Is<IMessageHandlerInvoker>(invoker => invoker.MessageType == typeof(FakeCommand))), Times.Once);
             }
 
+            [Test]
+            public async Task should_wait_for_unsubscribe_to_complete_before_adding_new_subscriptions()
+            {
+                _bus.Start();
+
+                _directoryMock.Setup(i => i.UpdateSubscriptionsAsync(It.IsAny<IBus>(), It.IsAny<IEnumerable<SubscriptionsForType>>()))
+                              .Returns(Task.CompletedTask);
+
+                var subA = await _bus.SubscribeAsync(Subscription.Any<FakeCommand>(), msg => { }).ConfigureAwait(true);
+
+                var unsubscribeTcs = new TaskCompletionSource<object>();
+                var unsubscribeSent = false;
+                _directoryMock.Setup(i => i.UpdateSubscriptionsAsync(It.IsAny<IBus>(), It.IsAny<IEnumerable<SubscriptionsForType>>()))
+                              .Callback(() => unsubscribeSent = true)
+                              .Returns(unsubscribeTcs.Task);
+
+                subA.Dispose();
+                Wait.Until(() => unsubscribeSent, 2.Seconds());
+
+                var newSubscribeSent = false;
+                _directoryMock.Setup(i => i.UpdateSubscriptionsAsync(It.IsAny<IBus>(), It.IsAny<IEnumerable<SubscriptionsForType>>()))
+                              .Callback(() => newSubscribeSent = true)
+                              .Returns(Task.CompletedTask);
+
+                var subBTask = _bus.SubscribeAsync(Subscription.Any<FakeCommand>(), msg => { });
+
+                Thread.Sleep(200);
+                newSubscribeSent.ShouldBeFalse();
+
+                unsubscribeTcs.SetResult(null);
+                Wait.Until(() => newSubscribeSent, 2.Seconds());
+
+                await subBTask.ConfigureAwait(true);
+            }
+
             [Test]
             [Ignore("The implementation is non trivial and will be dealt with later")]
             public void subscriptions_sent_to_the_directory_should_always_be_more_recent_than_the_previous()