fixed tests

Tests/MQTTnet.Core.Tests/TestServerExtensions.cs

@@ -0,0 +1,38 @@
+using MQTTnet.Client;
+using MQTTnet.Server;
+using System;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Core.Tests
+{
+    public static class TestServerExtensions
+    {
+        /// <summary>
+        /// 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) 
+        {
+            var tcs = new TaskCompletionSource<object>();
+
+            EventHandler<MqttApplicationMessageReceivedEventArgs> handler = (sender, args) =>
+            {
+                if (args.ApplicationMessage.Topic == message.Topic)
+                {
+                    tcs.SetResult(true);
+                }
+            };
+            server.ApplicationMessageReceived += handler;
+            
+            try
+            {
+                await client.PublishAsync(message);
+                await tcs.Task;
+            }
+            finally
+            {
+                server.ApplicationMessageReceived -= handler;
+            }
+        }
+    }
+}