diff --git a/Tests/MQTTnet.Core.Tests/MqttServerTests.cs b/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
index 0404ccc..fc40377 100644
--- a/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
+++ b/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
@@ -5,6 +5,7 @@ using MQTTnet.Protocol;
 using MQTTnet.Server;
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -98,11 +99,11 @@ namespace MQTTnet.Core.Tests
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
 
                 var message = new MqttApplicationMessageBuilder().WithTopic("a").WithAtLeastOnceQoS().Build();
-                
+
                 await c2.PublishAsync(message);
                 await Task.Delay(1000);
                 Assert.AreEqual(0, receivedMessagesCount);
-                
+
                 var subscribeEventCalled = false;
                 s.ClientSubscribedTopic += (_, e) =>
                     {
@@ -116,7 +117,7 @@ namespace MQTTnet.Core.Tests
                 await c2.PublishAsync(message);
                 await Task.Delay(500);
                 Assert.AreEqual(1, receivedMessagesCount);
-                
+
                 var unsubscribeEventCalled = false;
                 s.ClientUnsubscribedTopic += (_, e) =>
                 {
@@ -234,7 +235,7 @@ namespace MQTTnet.Core.Tests
                 await c1.PublishAsync(message);
             }
         }
-        
+
         [TestMethod]
         public async Task MqttServer_ShutdownDisconnectsClientsGracefully()
         {
@@ -303,6 +304,57 @@ namespace MQTTnet.Core.Tests
             Assert.AreEqual(clientConnectedCalled, clientDisconnectedCalled);
         }
 
+        [TestMethod]
+        public async Task MqttServer_LotsOfRetainedMessages()
+        {
+            const int ClientCount = 100;
+
+            var server = new MqttFactory().CreateMqttServer();
+            try
+            {
+                await server.StartAsync(new MqttServerOptionsBuilder().Build());
+
+                Parallel.For(
+                    0,
+                    ClientCount,
+                    new ParallelOptions { MaxDegreeOfParallelism = 10 },
+                    i =>
+                {
+                    using (var client = new MqttFactory().CreateMqttClient())
+                    {
+                        client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build())
+                            .GetAwaiter().GetResult();
+
+                        for (var j = 0; j < 10; j++)
+                        {
+                            // Clear retained message.
+                            client.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("r" + i)
+                                .WithPayload(new byte[0]).WithRetainFlag().Build()).GetAwaiter().GetResult();
+
+                            // Set retained message.
+                            client.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("r" + i)
+                                .WithPayload("value" + j).WithRetainFlag().Build()).GetAwaiter().GetResult();
+                        }
+
+                        client.DisconnectAsync().GetAwaiter().GetResult();
+                    }
+                });
+
+                var retainedMessages = server.GetRetainedMessages();
+
+                Assert.AreEqual(ClientCount, retainedMessages.Count);
+
+                for (var i = 0; i < ClientCount; i++)
+                {
+                    Assert.IsTrue(retainedMessages.Any(m => m.Topic == "r" + i));
+                }
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+        }
+
         [TestMethod]
         public async Task MqttServer_RetainedMessagesFlow()
         {
@@ -568,7 +620,7 @@ namespace MQTTnet.Core.Tests
 
                 await server.StartAsync(options);
 
-                
+
                 var clientOptions = new MqttClientOptionsBuilder()
                     .WithTcpServer("localhost").Build();
 
@@ -593,7 +645,7 @@ namespace MQTTnet.Core.Tests
             {
                 await client.DisconnectAsync();
                 await server.StopAsync();
-                
+
                 client.Dispose();
             }
         }
@@ -646,6 +698,33 @@ namespace MQTTnet.Core.Tests
             Assert.IsFalse(connecteCalledBeforeConnectedClients, "ClientConnected was called before ClientDisconnect was called");
         }
 
+
+        [TestMethod]
+        public async Task MqttServer_StopAndRestart()
+        {
+            var server = new MqttFactory().CreateMqttServer();
+            await server.StartAsync(new MqttServerOptions());
+
+            var client = new MqttFactory().CreateMqttClient();
+            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+            await server.StopAsync();
+
+            try
+            {
+                var client2 = new MqttFactory().CreateMqttClient();
+                await client2.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+                Assert.Fail("Connecting should fail.");
+            }
+            catch (Exception)
+            {
+            }
+
+            await server.StartAsync(new MqttServerOptions());
+            var client3 = new MqttFactory().CreateMqttClient();
+            await client3.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+        }
+
         private class TestStorage : IMqttServerStorage
         {
             public IList<MqttApplicationMessage> Messages = new List<MqttApplicationMessage>();
diff --git a/Tests/MQTTnet.Core.Tests/RoundtripTimeTests.cs b/Tests/MQTTnet.Core.Tests/RoundtripTimeTests.cs
new file mode 100644
index 0000000..7b5ad77
--- /dev/null
+++ b/Tests/MQTTnet.Core.Tests/RoundtripTimeTests.cs
@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Server;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class RoundtripTimeTests
+    {
+        [TestMethod]
+        public async Task Round_Trip_Time()
+        {
+            var factory = new MqttFactory();
+            var server = factory.CreateMqttServer();
+            var receiverClient = factory.CreateMqttClient();
+            var senderClient = factory.CreateMqttClient();
+
+            await server.StartAsync(new MqttServerOptionsBuilder().Build());
+
+            await receiverClient.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+            await receiverClient.SubscribeAsync("#");
+
+            await senderClient.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+            TaskCompletionSource<string> response = null;
+
+            receiverClient.ApplicationMessageReceived += (sender, args) =>
+            {
+                response?.SetResult(args.ApplicationMessage.ConvertPayloadToString());
+            };
+
+            var times = new List<TimeSpan>();
+            var stopwatch = Stopwatch.StartNew();
+
+            for (var i = 0; i < 100; i++)
+            {
+                response = new TaskCompletionSource<string>();
+                await senderClient.PublishAsync("test", DateTime.UtcNow.Ticks.ToString());
+                response.Task.GetAwaiter().GetResult();
+
+                stopwatch.Stop();
+                times.Add(stopwatch.Elapsed);
+                stopwatch.Restart();
+            }           
+        }
+    }
+}
diff --git a/Tests/MQTTnet.Core.Tests/TestServerExtensions.cs b/Tests/MQTTnet.Core.Tests/TestServerExtensions.cs
index cbb278c..7636b1a 100644
--- a/Tests/MQTTnet.Core.Tests/TestServerExtensions.cs
+++ b/Tests/MQTTnet.Core.Tests/TestServerExtensions.cs
@@ -11,19 +11,20 @@ namespace MQTTnet.Core.Tests
         /// publishes a message with a client and waits in the server until a message with the same topic is received
         /// </summary>
         /// <returns></returns>
-        public static async Task PublishAndWaitForAsync(this IMqttClient client, IMqttServer server, MqttApplicationMessage message) 
+        public static async Task PublishAndWaitForAsync(this IMqttClient client, IMqttServer server, MqttApplicationMessage message)
         {
             var tcs = new TaskCompletionSource<object>();
 
-            EventHandler<MqttApplicationMessageReceivedEventArgs> handler = (sender, args) =>
+            void Handler(object sender, MqttApplicationMessageReceivedEventArgs args)
             {
                 if (args.ApplicationMessage.Topic == message.Topic)
                 {
                     tcs.SetResult(true);
                 }
-            };
-            server.ApplicationMessageReceived += handler;
-            
+            }
+
+            server.ApplicationMessageReceived += Handler;
+
             try
             {
                 await client.PublishAsync(message).ConfigureAwait(false);
@@ -31,7 +32,7 @@ namespace MQTTnet.Core.Tests
             }
             finally
             {
-                server.ApplicationMessageReceived -= handler;
+                server.ApplicationMessageReceived -= Handler;
             }
         }
     }