Only allow one runner at a time per connection to the agent by the protocol design

src/NUnitEngine/nunit.engine.core/Agents/RemoteTestAgent.cs

@@ -38,12 +38,13 @@ namespace NUnit.Engine.Agents
     /// to it. Rather, it reports back to the sponsoring TestAgency upon
     /// startup so that the agency may in turn provide it to clients for use.
     /// </summary>
-    public class RemoteTestAgent : TestAgent, ITestEngineRunner
+    public class RemoteTestAgent : MarshalByRefObject, ITestAgent, IDisposable, ITestEngineRunner
     {
         private static readonly Logger log = InternalTrace.GetLogger(typeof(RemoteTestAgent));
 
         private readonly Guid _agentId;
         private readonly string _agencyUrl;
+        private readonly IServiceLocator _services;
 
         private ITestEngineRunner _runner;
         private TestPackage _package;
@@ -57,21 +58,34 @@ public class RemoteTestAgent : TestAgent, ITestEngineRunner
         /// Construct a RemoteTestAgent
         /// </summary>
         public RemoteTestAgent(Guid agentId, string agencyUrl, IServiceLocator services)
-            : base(services)
         {
             _agentId = agentId;
             _agencyUrl = agencyUrl;
+            _services = services;
+        }
+
+        /// <summary>
+        /// Overridden to cause object to live indefinitely
+        /// </summary>
+        public override object InitializeLifetimeService()
+        {
+            return null;
+        }
+
+        public void Dispose()
+        {
+            ShutDown();
         }
 
         public int ProcessId
         {
             get { return System.Diagnostics.Process.GetCurrentProcess().Id; }
         }
 
-        public override ITestEngineRunner CreateRunner(TestPackage package)
+        public ITestEngineRunner CreateRunner(TestPackage package)
         {
             _package = package;
-            _runner = Services.GetService<ITestRunnerFactory>().MakeTestRunner(_package);
+            _runner = _services.GetService<ITestRunnerFactory>().MakeTestRunner(_package);
             return this;
         }
 
@@ -107,7 +121,7 @@ public bool Start()
             return true;
         }
 
-        public override void Stop()
+        public void ShutDown()
         {
             log.Info("Stopping");
 

src/NUnitEngine/nunit.engine.core/ITestAgent.cs

@@ -31,7 +31,7 @@ public interface ITestAgent
         /// <summary>
         /// Stops the agent, releasing any resources
         /// </summary>
-        void Stop();
+        void ShutDown();
 
         /// <summary>
         ///  Creates a test runner

src/NUnitEngine/nunit.engine.tests/Services/AgentStoreTests.DummyTestAgent.cs

@@ -40,7 +40,7 @@ public bool Start()
                 throw new NotImplementedException();
             }
 
-            public void Stop()
+            public void ShutDown()
             {
                 throw new NotImplementedException();
             }

src/NUnitEngine/nunit.engine/Services/TestAgency.cs

@@ -202,7 +202,7 @@ private void Release(Guid agentId, ITestAgent agent)
                 try
                 {
                     log.Debug("Stopping remote agent");
-                    agent.Stop();
+                    agent.ShutDown();
                 }
                 catch (SocketException ex)
                 {