fixed disconnect to be triggered just once

Tests/MQTTnet.Core.Tests/MqttClientTests.cs

@@ -1,4 +1,5 @@
-using System.Net.Sockets;
+using System;
+using System.Net.Sockets;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
@@ -16,10 +17,10 @@ namespace MQTTnet.Core.Tests
             var factory = new MqttFactory();
             var client = factory.CreateMqttClient();
 
-            var exceptionIsCorrect = false;
+            Exception ex = null;
             client.Disconnected += (s, e) =>
             {
-                exceptionIsCorrect = e.Exception is MqttCommunicationException c && c.InnerException is SocketException;
+                ex = e.Exception;
             };
 
             try
@@ -29,8 +30,10 @@ namespace MQTTnet.Core.Tests
             catch
             {
             }
-            
-            Assert.IsTrue(exceptionIsCorrect);
+
+            Assert.IsNotNull(ex);
+            Assert.IsInstanceOfType(ex, typeof(MqttCommunicationException));
+            Assert.IsInstanceOfType(ex.InnerException, typeof(SocketException));
         }
     }
 }

Tests/MQTTnet.Core.Tests/MqttServerTests.cs

@@ -244,12 +244,12 @@ namespace MQTTnet.Core.Tests
                 .WithTcpServer("localhost")
                 .Build();
 
-            bool disconnectCalled = false;
+            var disconnectCalled = 0;
 
             await s.StartAsync(new MqttServerOptions());
 
             var c1 = new MqttFactory().CreateMqttClient();
-            c1.Disconnected += (sender, args) => disconnectCalled = true;
+            c1.Disconnected += (sender, args) => disconnectCalled++;
 
             await c1.ConnectAsync(clientOptions);
 
@@ -259,7 +259,7 @@ namespace MQTTnet.Core.Tests
 
             await Task.Delay(100);
 
-            Assert.IsTrue(disconnectCalled);
+            Assert.AreEqual(1, disconnectCalled);
         }
 
         [TestMethod]