Missing Cancel Implementation

src/Microsoft.TestPlatform.CommunicationUtilities/Interfaces/ITestRequestSender.cs

@@ -87,6 +87,11 @@ public interface ITestRequestSender : IDisposable
         /// </summary>
         void SendTestRunAbort();
 
+        /// <summary>
+        /// Send the request to cancel the test discovery
+        /// </summary>
+        void SendTestDiscoveryCancel();
+
         /// <summary>
         /// Handle client process exit
         /// </summary>

src/Microsoft.TestPlatform.CommunicationUtilities/TestRequestSender.cs

@@ -317,6 +317,23 @@ public void StartTestRun(TestRunCriteriaWithTests runCriteria, ITestRunEventsHan
             this.channel.Send(message);
         }
 
+        /// <inheritdoc />
+        public void SendTestDiscoveryCancel()
+        {
+            if (this.IsOperationComplete())
+            {
+                EqtTrace.Verbose("TestRequestSender: SendTestDiscoveryCancel: Operation is already complete. Skip error message.");
+                return;
+            }
+
+            if (EqtTrace.IsVerboseEnabled)
+            {
+                EqtTrace.Verbose("TestRequestSender.SendTestDiscoveryCancel: Sending test discovery cancel.");
+            }
+
+            this.channel?.Send(this.dataSerializer.SerializeMessage(MessageType.CancelDiscovery));
+        }
+
         /// <inheritdoc />
         public void SendTestRunCancel()
         {

src/Microsoft.TestPlatform.CrossPlatEngine/Client/ProxyDiscoveryManager.cs

@@ -140,7 +140,13 @@ public void DiscoverTests(DiscoveryCriteria discoveryCriteria, ITestDiscoveryEve
         /// <inheritdoc/>
         public void Abort()
         {
-            // This is no-op for the moment. There is no discovery abort message?
+            // Cancel fast, try to stop testhost deployment/launch
+            this.CancellationTokenSource.Cancel();
+
+            if (this.isCommunicationEstablished)
+            {
+                this.RequestSender.SendTestDiscoveryCancel();
+            }
         }
 
         /// <inheritdoc/>

src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs

@@ -318,6 +318,12 @@ public void OnMessageReceived(object sender, MessageReceivedEventArgs messageRec
                         break;
                     }
 
+                case MessageType.CancelDiscovery:
+                    jobQueue.Pause();
+                    this.testHostManagerFactoryReady.Wait();
+                    testHostManagerFactory.GetDiscoveryManager().Abort();
+                    break;
+
                 case MessageType.CancelTestRun:
                     jobQueue.Pause();
                     this.testHostManagerFactoryReady.Wait();

test/Microsoft.TestPlatform.CommunicationUtilities.UnitTests/TestRequestSenderTests.cs

@@ -202,6 +202,19 @@ public void EndSessionShouldNotSendTestRunAbortMessageIfClientDisconnected()
             this.mockChannel.Verify(mockChannel => mockChannel.Send(MessageType.CancelTestRun), Times.Never);
         }
 
+        [TestMethod]
+        public void SendTestDiscoveryCancelShouldSendTestDiscoveryCancelMessage()
+        {
+            var serializedCancelMessage = "Message : TestDiscovery.Cancel";
+            this.SetupFakeCommunicationChannel();
+            this.testRequestSender.DiscoverTests(new DiscoveryCriteria(), this.mockDiscoveryEventsHandler.Object);
+            this.mockDataSerializer.Setup(ds => ds.SerializeMessage(MessageType.CancelDiscovery)).Returns(serializedCancelMessage);
+
+            this.testRequestSender.SendTestDiscoveryCancel();
+
+            this.mockChannel.Verify(mockChannel => mockChannel.Send(serializedCancelMessage), Times.Once);
+        }
+
         [DataTestMethod]
         [DataRow("")]
         [DataRow(" ")]

test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/Client/ProxyDiscoveryManagerTests.cs

@@ -493,6 +493,21 @@ public void DiscoveryManagerShouldPassOnHandleLogMessage()
             mockTestDiscoveryEventsHandler.Verify(mtdeh => mtdeh.HandleLogMessage(It.IsAny<TestMessageLevel>(), It.IsAny<string>()), Times.Once);
         }
 
+        [TestMethod]
+        public void AbortShouldSendTestDiscoveryCancelIfCommunicationSuccessful()
+        {
+            var mockTestDiscoveryEventsHandler = new Mock<ITestDiscoveryEventsHandler2>();
+            this.mockRequestSender.Setup(s => s.WaitForRequestHandlerConnection(It.IsAny<int>(), It.IsAny<CancellationToken>())).Returns(true);
+
+            Mock<ITestRunEventsHandler> mockTestRunEventsHandler = new Mock<ITestRunEventsHandler>();
+
+            this.testDiscoveryManager.DiscoverTests(this.discoveryCriteria, mockTestDiscoveryEventsHandler.Object);
+
+            this.testDiscoveryManager.Abort();
+
+            this.mockRequestSender.Verify(s => s.SendTestDiscoveryCancel(), Times.Once);
+        }
+
         private void InvokeAndVerifyDiscoverTests(bool skipDefaultAdapters)
         {
             TestPluginCache.Instance = null;

test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/EventHandlers/TestRequestHandlerTests.cs

@@ -286,7 +286,17 @@ public void ProcessRequestsExecutionCancelShouldCancelTestRun()
             this.SendSessionEnd();
         }
 
-        // ProcessRequestsExecutionCancelShouldStopRequestProcessing
+        [TestMethod]
+        public void ProcessRequestsDiscoveryCancelShouldCancelDiscovery()
+        {
+            var message = this.dataSerializer.SerializePayload(MessageType.CancelDiscovery, string.Empty);
+
+            this.ProcessRequestsAsync(this.mockTestHostManagerFactory.Object);
+            this.SendMessageOnChannel(message);
+
+            mockDiscoveryManager.Verify(dm => dm.Abort(), Times.Once);
+            this.SendSessionEnd();
+        }
 
         [TestMethod]
         public void ProcessRequestsExecutionLaunchAdapterProcessWithDebuggerShouldSendAckMessage()
@@ -312,8 +322,6 @@ public void ProcessRequestsExecutionAbortShouldStopTestRun()
             this.SendSessionEnd();
         }
 
-        // ProcessRequestsExecutionAbortShouldStopRequestProcessing
-
         [TestMethod]
         public void SendExecutionCompleteShouldSendTestRunCompletePayloadOnChannel()
         {