Improve Unit Tests.

Tests/MQTTnet.Core.Tests/Mockups/TestEnvironment.cs

@@ -105,6 +105,7 @@ namespace MQTTnet.Tests.Mockups
             Server = new TestServerWrapper(_mqttFactory.CreateMqttServer(ServerLogger), TestContext, this);
 
             options.WithDefaultEndpointPort(ServerPort);
+            options.WithMaxPendingMessagesPerClient(int.MaxValue);
 
             await Server.StartAsync(options.Build()).ConfigureAwait(false);
 

Tests/MQTTnet.Core.Tests/Server_Tests.cs

@@ -304,7 +304,7 @@ namespace MQTTnet.Tests
                     await c2.PublishAsync(messageBuilder.Build()).ConfigureAwait(false);
                 }
 
-                SpinWait.SpinUntil(() => receivedMessagesCount == 500, TimeSpan.FromSeconds(15));
+                SpinWait.SpinUntil(() => receivedMessagesCount == 500, TimeSpan.FromSeconds(20));
 
                 Assert.AreEqual(500, receivedMessagesCount);
             }