Add test for simple server and client execution.

Tests/MQTTnet.TestApp.NetCore/Program.cs

@@ -20,6 +20,7 @@ namespace MQTTnet.TestApp.NetCore
             Console.WriteLine("3 = Start performance test");
             Console.WriteLine("4 = Start managed client");
             Console.WriteLine("5 = Start public broker test");
+            Console.WriteLine("6 = Start server & client");
 
             var pressedKey = Console.ReadKey(true);
             if (pressedKey.KeyChar == '1')
@@ -42,6 +43,10 @@ namespace MQTTnet.TestApp.NetCore
             {
                 Task.Run(PublicBrokerTest.RunAsync);
             }
+            else if (pressedKey.KeyChar == '6')
+            {
+                Task.Run(ServerAndClientTest.RunAsync);
+            }
 
             Thread.Sleep(Timeout.Infinite);
         }

Tests/MQTTnet.TestApp.NetCore/ServerAndClientTest.cs

@@ -0,0 +1,27 @@
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Client;
+using MQTTnet.Server;
+
+namespace MQTTnet.TestApp.NetCore
+{
+    public static class ServerAndClientTest
+    {
+        public static async Task RunAsync()
+        {
+            MqttNetConsoleLogger.ForwardToConsole();
+
+            var factory = new MqttFactory();
+            var server = factory.CreateMqttServer();
+            var client = factory.CreateMqttClient();
+
+            var serverOptions = new MqttServerOptionsBuilder().Build();
+            await server.StartAsync(serverOptions);
+
+            var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost").Build();
+            await client.ConnectAsync(clientOptions);
+
+            await Task.Delay(Timeout.Infinite);
+        }
+    }
+}