1595 object disposed exception in unit test handle parallel connection attempts (#1610)

Source/MQTTnet.Tests/Helpers/MqttPacketWriterExtensions.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using MQTTnet.Formatter;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Tests.Helpers
+{
+    public static class MqttPacketWriterExtensions
+    {
+        public static byte[] AddMqttHeader(this MqttBufferWriter writer, MqttControlPacketType header, byte[] body)
+        {
+            writer.WriteByte(MqttBufferWriter.BuildFixedHeader(header));
+            writer.WriteVariableByteInteger((uint)body.Length);
+            writer.WriteBinary(body, 0, body.Length);
+            return writer.GetBuffer();
+        }
+    }
+}