Add nuget support

Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapter.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Tests
+{
+    public class TestMqttCommunicationAdapter : IMqttCommunicationAdapter
+    {
+        private readonly BlockingCollection<MqttBasePacket> _incomingPackets = new BlockingCollection<MqttBasePacket>();
+
+        public TestMqttCommunicationAdapter Partner { get; set; }
+
+        public async Task ConnectAsync(MqttClientOptions options, TimeSpan timeout)
+        {
+            await Task.FromResult(0);
+        }
+
+        public async Task DisconnectAsync()
+        {
+            await Task.FromResult(0);
+        }
+
+        public async Task SendPacketAsync(MqttBasePacket packet, TimeSpan timeout)
+        {
+            ThrowIfPartnerIsNull();
+
+            Partner.SendPacketInternal(packet);
+            await Task.FromResult(0);
+        }
+
+        public async Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout)
+        {
+            ThrowIfPartnerIsNull();
+
+            return await Task.Run(() => _incomingPackets.Take());
+        }
+
+        private void SendPacketInternal(MqttBasePacket packet)
+        {
+            if (packet == null) throw new ArgumentNullException(nameof(packet));
+
+            _incomingPackets.Add(packet);
+        }
+
+        private void ThrowIfPartnerIsNull()
+        {
+            if (Partner == null)
+            {
+                throw new InvalidOperationException("Partner is not set.");
+            }
+        }
+    }
+}