Modifying the reporting channels to make the AdapterChannel a client and leave the TestRunnerChannel a server. This will prevent port conflicts between dotnet test and the Adapter (VS) due to race conditions.

Added E2E tests for dotnet test interactions with an adapter (design time).

test/dotnet-test.Tests/Adapter.cs

@@ -0,0 +1,177 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading;
+using Microsoft.Extensions.Testing.Abstractions;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using System.Diagnostics;
+
+namespace Microsoft.Dotnet.Tools.Test.Tests
+{
+    public class Adapter : IDisposable
+    {
+        private readonly string _startMessage;
+        private BinaryWriter _writer;
+        private BinaryReader _reader;
+        private Socket _socket;
+        private Socket _listenSocket;
+
+        public IDictionary<string, List<Message>> Messages { get; }
+
+        public int Port { get; private set; }
+
+        public Adapter(string startMessage)
+        {
+            _startMessage = startMessage;
+            Messages = new Dictionary<string, List<Message>>();
+
+            _listenSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            var endpoint = new IPEndPoint(IPAddress.Loopback, 0);
+            _listenSocket.Bind(endpoint);
+
+            Port = ((IPEndPoint)_listenSocket.LocalEndPoint).Port;
+        }
+
+        public void Listen()
+        {
+            var listenThread = new Thread(() =>
+            {
+                using (_listenSocket)
+                {
+                    _listenSocket.Listen(1);
+                    _socket = _listenSocket.Accept();
+                }
+
+                var stream = new NetworkStream(_socket);
+                _writer = new BinaryWriter(stream);
+                _reader = new BinaryReader(stream);
+
+                ReadMessages();
+            })
+            {
+                IsBackground = true
+            };
+
+            listenThread.Start();
+        }
+
+        public void Send(string messageType)
+        {
+            lock (_writer)
+            {
+                _writer.Write(JsonConvert.SerializeObject(new
+                {
+                    MessageType = messageType,
+                    PayLoad = JToken.FromObject(new
+                    {
+                    })
+                }));
+            }
+        }
+
+        private void ReadMessages()
+        {
+            while (true)
+            {
+                try
+                {
+                    var message = GetMessage();
+
+                    StoreMessage(message);
+
+                    if (HandleMessage(message))
+                    {
+                        break;
+                    }
+                }
+                catch (Exception)
+                {
+                    throw;
+                }
+            }
+        }
+
+        private void StoreMessage(Message message)
+        {
+            if (!Messages.ContainsKey(message.MessageType))
+            {
+                Messages.Add(message.MessageType, new List<Message>());
+            }
+
+            Messages[message.MessageType].Add(message);
+        }
+
+        private bool HandleMessage(Message message)
+        {
+            if (message.MessageType == "TestSession.Connected")
+            {
+                Send(_startMessage);
+            }
+
+            if (message.MessageType == "TestExecution.TestRunnerProcessStartInfo")
+            {
+                StartTestRunner(message.Payload.ToObject<TestStartInfo>());
+            }
+
+            if (message.MessageType == "TestDiscovery.Completed")
+            {
+                Send("TestSession.Terminate");
+                return true;
+            }
+
+            if (message.MessageType == "TestExecution.Completed")
+            {
+                Send("TestSession.Terminate");
+                return true;
+            }
+
+            return false;
+        }
+
+        private static void StartTestRunner(TestStartInfo testPsiInfo)
+        {
+            var testPsi = new ProcessStartInfo(testPsiInfo.FileName, testPsiInfo.Arguments);
+            testPsi.RedirectStandardOutput = true;
+            testPsi.UseShellExecute = false;
+            var testProcess = new Process
+            {
+                StartInfo = testPsi
+            };
+
+            var testProcessThread = new Thread(() => { testProcess.Start(); })
+            {
+                IsBackground = true
+            };
+            testProcessThread.Start();
+        }
+
+        private Message GetMessage()
+        {
+            var rawMessage = _reader.ReadString();
+            Console.WriteLine("\nRECEIVING MESSAGE:");
+            Console.WriteLine($"{rawMessage}");
+            Console.WriteLine($"==============================\n");
+
+            var message = JsonConvert.DeserializeObject<Message>(rawMessage);
+            return message;
+        }
+
+        public void Dispose()
+        {
+            _socket?.Dispose();
+        }
+
+        private class TestStartInfo
+        {
+            public string FileName { get; set; }
+
+            public string Arguments { get; set; }
+        }
+    }
+}