diff --git a/TestPlatform.sln b/TestPlatform.sln
index 3849fef928..4db14778e0 100644
--- a/TestPlatform.sln
+++ b/TestPlatform.sln
@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 15
-VisualStudioVersion = 15.0.26730.16
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.29025.244
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{ED0C35EB-7F31-4841-A24F-8EB708FFA959}"
 EndProject
@@ -170,6 +170,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SettingsMigrator", "src\Set
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SettingsMigrator.UnitTests", "test\SettingsMigrator.UnitTests\SettingsMigrator.UnitTests.csproj", "{E7D4921C-F12D-4E1C-85AC-8B7F91C59B0E}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "DiscoveryTestProject", "test\TestAssets\DiscoveryTestProject\DiscoveryTestProject.csproj", "{D16ACC60-52F8-4912-8870-5733A9F6852D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -852,6 +854,18 @@ Global
 		{E7D4921C-F12D-4E1C-85AC-8B7F91C59B0E}.Release|x64.Build.0 = Release|Any CPU
 		{E7D4921C-F12D-4E1C-85AC-8B7F91C59B0E}.Release|x86.ActiveCfg = Release|Any CPU
 		{E7D4921C-F12D-4E1C-85AC-8B7F91C59B0E}.Release|x86.Build.0 = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|x64.Build.0 = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Debug|x86.Build.0 = Debug|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|x64.ActiveCfg = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|x64.Build.0 = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|x86.ActiveCfg = Release|Any CPU
+		{D16ACC60-52F8-4912-8870-5733A9F6852D}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -925,6 +939,7 @@ Global
 		{A7E2261B-B2E6-4CBF-983F-E3A3FF8E52E3} = {D9A30E32-D466-4EC5-B4F2-62E17562279B}
 		{69F5FF81-5615-4F06-B83C-FCF979BB84CA} = {ED0C35EB-7F31-4841-A24F-8EB708FFA959}
 		{E7D4921C-F12D-4E1C-85AC-8B7F91C59B0E} = {B27FAFDF-2DBA-4AB0-BA85-FD5F21D359D6}
+		{D16ACC60-52F8-4912-8870-5733A9F6852D} = {8DA7CBD9-F17E-41B6-90C4-CFF55848A25A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {0541B30C-FF51-4E28-B172-83F5F3934BCD}
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
index 2c80c6ef3e..41e6b135ae 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
@@ -196,6 +196,12 @@ private void ProcessRequests(ITestRequestManager testRequestManager)
                                 break;
                             }
 
+                        case MessageType.CancelDiscovery:
+                            {
+                                testRequestManager.CancelDiscovery();
+                                break;
+                            }
+
                         case MessageType.CancelTestRun:
                             {
                                 testRequestManager.CancelTestRun();
diff --git a/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs b/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
index db1e20024a..d23975afed 100644
--- a/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
+++ b/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
@@ -53,5 +53,10 @@ public interface ITestRequestManager : IDisposable
         /// Abort the current TestRun
         /// </summary>
         void AbortTestRun();
+
+        /// <summary>
+        /// Cancels the current discovery request
+        /// </summary>
+        void CancelDiscovery();
     }
 }
diff --git a/src/Microsoft.TestPlatform.CommunicationUtilities/Messages/MessageType.cs b/src/Microsoft.TestPlatform.CommunicationUtilities/Messages/MessageType.cs
index 099a15d6ad..b7eb93ded8 100644
--- a/src/Microsoft.TestPlatform.CommunicationUtilities/Messages/MessageType.cs
+++ b/src/Microsoft.TestPlatform.CommunicationUtilities/Messages/MessageType.cs
@@ -63,6 +63,11 @@ public static class MessageType
         /// </summary>
         public const string DiscoveryComplete = "TestDiscovery.Completed";
 
+        /// <summary>
+        /// Cancel Test Discovery
+        /// </summary>
+        public const string CancelDiscovery = "TestDiscovery.Cancel";
+
         /// <summary>
         /// The session start.
         /// </summary>
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscovererEnumerator.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscovererEnumerator.cs
index 4ab2a1aa17..48666d0c3d 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscovererEnumerator.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscovererEnumerator.cs
@@ -10,7 +10,7 @@ namespace Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Discovery
     using System.IO;
     using System.Linq;
     using System.Reflection;
-
+    using System.Threading;
     using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework;
     using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework.Utilities;
     using Microsoft.VisualStudio.TestPlatform.Common.Filtering;
@@ -33,44 +33,59 @@ namespace Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Discovery
     /// </summary>
     internal class DiscovererEnumerator
     {
-        private DiscoveryResultCache discoveryResultCache;
-        private ITestPlatformEventSource testPlatformEventSource;
-        private IRequestData requestData;
-        private IAssemblyProperties assemblyProperties;
+        private readonly DiscoveryResultCache discoveryResultCache;
+        private readonly ITestPlatformEventSource testPlatformEventSource;
+        private readonly IRequestData requestData;
+        private readonly IAssemblyProperties assemblyProperties;
+        private readonly CancellationToken cancellationToken;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DiscovererEnumerator"/> class.
         /// </summary>
         /// <param name="requestData">The request data for providing discovery services and data.</param>
         /// <param name="discoveryResultCache"> The discovery result cache. </param>
-        /// <param name="metricsCollector">Metric Collector</param>
-        public DiscovererEnumerator(IRequestData requestData, DiscoveryResultCache discoveryResultCache) : this(requestData, discoveryResultCache, TestPlatformEventSource.Instance)
+        public DiscovererEnumerator(IRequestData requestData, DiscoveryResultCache discoveryResultCache, CancellationToken token)
+            : this(requestData, discoveryResultCache, TestPlatformEventSource.Instance, token)
         {
         }
 
-        internal DiscovererEnumerator(IRequestData requestData,
+        /// <summary>
+        /// Initializes a new instance of the <see cref="DiscovererEnumerator"/> class.
+        /// </summary>
+        /// <param name="requestData">The request data for providing discovery services and data.</param>
+        /// <param name="discoveryResultCache"> The discovery result cache. </param>
+        /// <param name="testPlatformEventSource">Telemetry events receiver</param>
+        /// <param name="token">Cancellation Token to abort discovery</param>
+        public DiscovererEnumerator(IRequestData requestData,
             DiscoveryResultCache discoveryResultCache,
-            ITestPlatformEventSource testPlatformEventSource)
+            ITestPlatformEventSource testPlatformEventSource,
+            CancellationToken token)
+            : this(requestData, discoveryResultCache, testPlatformEventSource, new AssemblyProperties(), token)
         {
-            this.discoveryResultCache = discoveryResultCache;
-            this.testPlatformEventSource = testPlatformEventSource;
-            this.requestData = requestData;
-            this.assemblyProperties = new AssemblyProperties();
         }
 
-        // Added this to make class testable, needed a PEHeader mocked Instance
-        internal DiscovererEnumerator(IRequestData requestData,
+        /// <summary>
+        /// Initializes a new instance of the <see cref="DiscovererEnumerator"/> class.
+        /// </summary>
+        /// <param name="requestData">The request data for providing discovery services and data.</param>
+        /// <param name="discoveryResultCache"> The discovery result cache. </param>
+        /// <param name="testPlatformEventSource">Telemetry events receiver</param>
+        /// <param name="assemblyProperties">Information on the assemblies being discovered</param>
+        /// <param name="token">Cancellation Token to abort discovery</param>
+        public DiscovererEnumerator(IRequestData requestData,
             DiscoveryResultCache discoveryResultCache,
             ITestPlatformEventSource testPlatformEventSource,
-            IAssemblyProperties assemblyProperties)
+            IAssemblyProperties assemblyProperties,
+            CancellationToken token)
         {
+            // Added this to make class testable, needed a PEHeader mocked Instance
             this.discoveryResultCache = discoveryResultCache;
             this.testPlatformEventSource = testPlatformEventSource;
             this.requestData = requestData;
             this.assemblyProperties = assemblyProperties;
+            this.cancellationToken = token;
         }
 
-
         /// <summary>
         /// Discovers tests from the sources.
         /// </summary>
@@ -78,14 +93,20 @@ internal DiscovererEnumerator(IRequestData requestData,
         /// <param name="settings"> The settings. </param>
         /// <param name="testCaseFilter"> The test case filter. </param>
         /// <param name="logger"> The logger. </param>
-        internal void LoadTests(IDictionary<string, IEnumerable<string>> testExtensionSourceMap, IRunSettings settings, string testCaseFilter, IMessageLogger logger)
+        public void LoadTests(IDictionary<string, IEnumerable<string>> testExtensionSourceMap, IRunSettings settings, string testCaseFilter, IMessageLogger logger)
         {
             this.testPlatformEventSource.DiscoveryStart();
-            foreach (var kvp in testExtensionSourceMap)
+            try
             {
-                this.LoadTestsFromAnExtension(kvp.Key, kvp.Value, settings, testCaseFilter, logger);
+                foreach (var kvp in testExtensionSourceMap)
+                {
+                    this.LoadTestsFromAnExtension(kvp.Key, kvp.Value, settings, testCaseFilter, logger);
+                }
+            }
+            finally
+            {
+                this.testPlatformEventSource.DiscoveryStop(this.discoveryResultCache.TotalDiscoveredTests);
             }
-            this.testPlatformEventSource.DiscoveryStop(this.discoveryResultCache.TotalDiscoveredTests);
         }
 
         /// <summary>
@@ -105,7 +126,7 @@ private void LoadTestsFromAnExtension(string extensionAssembly, IEnumerable<stri
             // Stopwatch to collect metrics
             var timeStart = DateTime.UtcNow;
 
-            var discovererToSourcesMap = DiscovererEnumerator.GetDiscovererToSourcesMap(extensionAssembly, sources, logger, this.assemblyProperties);
+            var discovererToSourcesMap = GetDiscovererToSourcesMap(extensionAssembly, sources, logger, this.assemblyProperties);
             var totalAdapterLoadTIme = DateTime.UtcNow - timeStart;
 
             // Collecting Data Point for TimeTaken to Load Adapters
@@ -117,30 +138,46 @@ private void LoadTestsFromAnExtension(string extensionAssembly, IEnumerable<stri
                 return;
             }
 
-            // Collecting Total Number of Adapters Discovered in Machine
-            this.requestData.MetricsCollection.Add(TelemetryDataConstants.NumberOfAdapterDiscoveredDuringDiscovery, discovererToSourcesMap.Keys.Count());
+            double totalTimeTakenByAdapters = 0;
+            double totalAdaptersUsed = 0;
+            try
+            {
+                // Collecting Total Number of Adapters Discovered in Machine
+                this.requestData.MetricsCollection.Add(TelemetryDataConstants.NumberOfAdapterDiscoveredDuringDiscovery, discovererToSourcesMap.Keys.Count());
 
-            var context = new DiscoveryContext { RunSettings = settings };
-            context.FilterExpressionWrapper = !string.IsNullOrEmpty(testCaseFilter) ? new FilterExpressionWrapper(testCaseFilter) : null;
+                var context = new DiscoveryContext { RunSettings = settings };
+                context.FilterExpressionWrapper = !string.IsNullOrEmpty(testCaseFilter) ? new FilterExpressionWrapper(testCaseFilter) : null;
 
-            // Set on the logger the TreatAdapterErrorAsWarning setting from runsettings.
-            this.SetAdapterLoggingSettings(logger, settings);
+                // Set on the logger the TreatAdapterErrorAsWarning setting from runsettings.
+                this.SetAdapterLoggingSettings(logger, settings);
 
-            var discoverySink = new TestCaseDiscoverySink(this.discoveryResultCache);
-            double totalTimeTakenByAdapters = 0;
-            double totalAdaptersUsed = 0;
+                var discoverySink = new TestCaseDiscoverySink(this.discoveryResultCache);
+                foreach (var discoverer in discovererToSourcesMap.Keys)
+                {
+                    if (this.cancellationToken.IsCancellationRequested)
+                    {
+                        EqtTrace.Info("DiscovererEnumerator.LoadTestsFromAnExtension: Cancellation Requested. Aborting the discovery");
+                        LogTestsDiscoveryCancellation(logger);
+                        return;
+                    }
+
+                    this.DiscoverTestsFromSingleDiscoverer(discoverer, discovererToSourcesMap, context, discoverySink, logger, ref totalAdaptersUsed, ref totalTimeTakenByAdapters);
+                }
 
-            foreach (var discoverer in discovererToSourcesMap.Keys)
-            {
-                this.DiscoverTestsFromSingleDiscoverer(discoverer, discovererToSourcesMap, context, discoverySink, logger, ref totalAdaptersUsed, ref totalTimeTakenByAdapters);
+                if (this.discoveryResultCache.TotalDiscoveredTests == 0)
+                {
+                    LogWarningOnNoTestsDiscovered(sources, testCaseFilter, logger);
+                }
             }
-
-            if (this.discoveryResultCache.TotalDiscoveredTests == 0)
+            finally
             {
-                DiscovererEnumerator.LogWarningOnNoTestsDiscovered(sources, testCaseFilter, logger);
+                this.CollectTelemetryAtEnd(totalTimeTakenByAdapters, totalAdaptersUsed);
             }
+        }
 
-            this.CollectTelemetryAtEnd(totalTimeTakenByAdapters, totalAdaptersUsed);
+        private void LogTestsDiscoveryCancellation(IMessageLogger logger)
+        {
+            logger.SendMessage(TestMessageLevel.Warning, CrossPlatEngineResources.TestDiscoveryCancelled);
         }
 
         private void CollectTelemetryAtEnd(double totalTimeTakenByAdapters, double totalAdaptersUsed)
@@ -427,8 +464,8 @@ private static bool IsAssembly(string filePath)
                 ".exe".Equals(fileExtension, StringComparison.OrdinalIgnoreCase);
         }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design",
+        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
+        [SuppressMessage("Microsoft.Design",
             "CA1006:DoNotNestGenericTypesInMemberSignatures")]
         private static IEnumerable<LazyExtension<ITestDiscoverer, ITestDiscovererCapabilities>> GetDiscoverers(
             string extensionAssembly,
@@ -436,7 +473,7 @@ private static IEnumerable<LazyExtension<ITestDiscoverer, ITestDiscovererCapabil
         {
             try
             {
-                if (string.IsNullOrEmpty(extensionAssembly) || string.Equals(extensionAssembly, ObjectModel.Constants.UnspecifiedAdapterPath))
+                if (string.IsNullOrEmpty(extensionAssembly) || string.Equals(extensionAssembly, Constants.UnspecifiedAdapterPath))
                 {
                     // full discovery.
                     return TestDiscoveryExtensionManager.Create().Discoverers;
@@ -448,10 +485,7 @@ private static IEnumerable<LazyExtension<ITestDiscoverer, ITestDiscovererCapabil
             }
             catch (Exception ex)
             {
-                EqtTrace.Error(
-                    "TestDiscoveryManager: LoadExtensions: Exception occured while loading extensions {0}",
-                    ex);
-
+                EqtTrace.Error($"TestDiscoveryManager: LoadExtensions: Exception occured while loading extensions {ex}");
                 if (throwOnError)
                 {
                     throw;
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscoveryManager.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscoveryManager.cs
index caa346090e..0f724688bf 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscoveryManager.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Discovery/DiscoveryManager.cs
@@ -9,7 +9,7 @@ namespace Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Discovery
     using System.Globalization;
     using System.IO;
     using System.Linq;
-
+    using System.Threading;
     using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework;
     using Microsoft.VisualStudio.TestPlatform.Common.Logging;
     using Microsoft.VisualStudio.TestPlatform.Common.Telemetry;
@@ -28,11 +28,12 @@ namespace Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Discovery
     /// </summary>
     public class DiscoveryManager : IDiscoveryManager
     {
-        private TestSessionMessageLogger sessionMessageLogger;
-        private ITestPlatformEventSource testPlatformEventSource;
-        private IRequestData requestData;
+        private readonly TestSessionMessageLogger sessionMessageLogger;
+        private readonly ITestPlatformEventSource testPlatformEventSource;
+        private readonly IRequestData requestData;
         private ITestDiscoveryEventsHandler2 testDiscoveryEventsHandler;
         private DiscoveryCriteria discoveryCriteria;
+        private readonly CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DiscoveryManager"/> class.
@@ -109,7 +110,7 @@ public void DiscoverTests(DiscoveryCriteria discoveryCriteria, ITestDiscoveryEve
                 // If there are sources to discover
                 if (verifiedExtensionSourceMap.Any())
                 {
-                    new DiscovererEnumerator(this.requestData, discoveryResultCache).LoadTests(
+                    new DiscovererEnumerator(this.requestData, discoveryResultCache, cancellationTokenSource.Token).LoadTests(
                         verifiedExtensionSourceMap,
                         RunSettingsUtilities.CreateAndInitializeRunSettings(discoveryCriteria.RunSettings),
                         discoveryCriteria.TestCaseFilter,
@@ -138,9 +139,10 @@ public void DiscoverTests(DiscoveryCriteria discoveryCriteria, ITestDiscoveryEve
 
                     // Collecting Total Tests Discovered
                     this.requestData.MetricsCollection.Add(TelemetryDataConstants.TotalTestsDiscovered, totalDiscoveredTestCount);
-
-                    var discoveryCompleteEventsArgs = new DiscoveryCompleteEventArgs(totalDiscoveredTestCount, false);
-                    discoveryCompleteEventsArgs.Metrics = this.requestData.MetricsCollection.Metrics;
+                    var discoveryCompleteEventsArgs = new DiscoveryCompleteEventArgs(totalDiscoveredTestCount, false)
+                    {
+                        Metrics = this.requestData.MetricsCollection.Metrics
+                    };
 
                     eventHandler.HandleDiscoveryComplete(discoveryCompleteEventsArgs, lastChunk);
                 }
@@ -161,7 +163,7 @@ public void DiscoverTests(DiscoveryCriteria discoveryCriteria, ITestDiscoveryEve
         /// </summary>
         public void Abort()
         {
-            // do nothing for now.
+            this.cancellationTokenSource.Cancel();
         }
 
         private void OnReportTestCases(IEnumerable<TestCase> testCases)
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.Designer.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.Designer.cs
index ee5729186a..29ba479681 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.Designer.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.Designer.cs
@@ -250,6 +250,15 @@ internal static string StringSeperator {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Discovery of tests cancelled..
+        /// </summary>
+        internal static string TestDiscoveryCancelled {
+            get {
+                return ResourceManager.GetString("TestDiscoveryCancelled", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Logging TestHost Diagnostics in file: {0}.
         /// </summary>
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.resx b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.resx
index f23a139ea2..8e51734589 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.resx
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/Resources.resx
@@ -195,4 +195,7 @@
   <data name="NoTestsAvailableForGivenTestCaseFilter" xml:space="preserve">
     <value>No test matches the given testcase filter `{0}` in {1}</value>
   </data>
+  <data name="TestDiscoveryCancelled" xml:space="preserve">
+    <value>Discovery of tests cancelled.</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.cs.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.cs.xlf
index 4b13ac29a5..e9ebcc811b 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.cs.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.cs.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Žádný test neodpovídá danému filtru testovacích případů {0} v: {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.de.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.de.xlf
index e00692696f..d0a5f20427 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.de.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.de.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Kein Test entspricht dem angegebenen Testfallfilter "{0}" in "{1}".</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.es.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.es.xlf
index e7aea95913..37c9a42691 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.es.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.es.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Ninguna prueba coincide con el filtro de casos de prueba proporcionado "{0}" en {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.fr.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.fr.xlf
index b1a935654b..d4b7d1a32f 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.fr.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.fr.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Aucun test ne correspond au filtre testcase donné `{0}` dans {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.it.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.it.xlf
index 572f77c4f4..67756aea99 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.it.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.it.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Nessun test corrisponde al filtro di test case specificato `{0}` in {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ja.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ja.xlf
index 63baf9e928..43be67f220 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ja.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ja.xlf
@@ -202,6 +202,11 @@
         <target state="translated">指定のテストケース フィルター `{0}` に一致するテストは {1} にありません</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ko.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ko.xlf
index e478788cae..bafed6bd6a 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ko.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ko.xlf
@@ -202,6 +202,11 @@
         <target state="translated">{1}에 지정된 테스트 사례 필터 `{0}`과(와) 일치하는 테스트가 없습니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pl.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pl.xlf
index 0665f698e4..815d170a08 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pl.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pl.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Żaden test nie jest zgodny z podanym filtrem przypadku testowego „{0}” w elemencie {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pt-BR.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pt-BR.xlf
index f7e0c55e08..3bfd15d201 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pt-BR.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.pt-BR.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Nenhum teste corresponde ao filtro de testcase `{0}` determinado no {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ru.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ru.xlf
index 56c800fdeb..68ba5c1ef9 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ru.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.ru.xlf
@@ -202,6 +202,11 @@
         <target state="translated">Нет тестов, соответствующих указанному фильтру тестовых случаев "{0}" в {1}</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.tr.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.tr.xlf
index 910fcb85b7..702cad8308 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.tr.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.tr.xlf
@@ -202,6 +202,11 @@
         <target state="translated">{1} içinde sunulan test çalışması filtresi `{0}` ile eşleşen test yok</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.xlf
index ae9f1b44ef..087be26de8 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.xlf
@@ -113,6 +113,11 @@
         <target state="new">No test is available for testcase filter `{0}` in {1}</target>
         <note></note>
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hans.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hans.xlf
index 8d1084dec9..b6f0fa3bb5 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hans.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hans.xlf
@@ -202,6 +202,11 @@
         <target state="translated">没有测试匹配 {1} 中的给定用例测试筛选器“{0}”</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hant.xlf b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hant.xlf
index c6bf1aef3a..5298bdc38b 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hant.xlf
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Resources/xlf/Resources.zh-Hant.xlf
@@ -202,6 +202,11 @@
         <target state="translated">沒有任何測試符合 {1} 中的指定 testcase 篩選 `{0}`</target>
         <note />
       </trans-unit>
+      <trans-unit id="TestDiscoveryCancelled">
+        <source>Discovery of tests cancelled.</source>
+        <target state="new">Discovery of tests cancelled.</target>
+        <note></note>
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file
diff --git a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/Interfaces/ITranslationLayerRequestSender.cs b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/Interfaces/ITranslationLayerRequestSender.cs
index a49522c7d7..bf8beeea6d 100644
--- a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/Interfaces/ITranslationLayerRequestSender.cs
+++ b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/Interfaces/ITranslationLayerRequestSender.cs
@@ -105,5 +105,10 @@ internal interface ITranslationLayerRequestSender : IDisposable
         /// On process exit unblocks communication waiting calls
         /// </summary>
         void OnProcessExited();
+
+        /// <summary>
+        /// Cancels the discovery of tests
+        /// </summary>
+        void CancelDiscovery();
     }
 }
diff --git a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleRequestSender.cs b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleRequestSender.cs
index ec2314770f..1f4222fea3 100644
--- a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleRequestSender.cs
+++ b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleRequestSender.cs
@@ -275,6 +275,12 @@ public void AbortTestRun()
             this.communicationManager.SendMessage(MessageType.AbortTestRun);
         }
 
+        /// <inheritdoc/>
+        public void CancelDiscovery()
+        {
+            this.communicationManager.SendMessage(MessageType.CancelDiscovery);
+        }
+
         /// <inheritdoc/>
         public void OnProcessExited()
         {
diff --git a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleWrapper.cs b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleWrapper.cs
index 99250c2b07..f340ef50e3 100644
--- a/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleWrapper.cs
+++ b/src/Microsoft.TestPlatform.VsTestConsole.TranslationLayer/VsTestConsoleWrapper.cs
@@ -166,8 +166,7 @@ public void DiscoverTests(IEnumerable<string> sources, string discoverySettings,
         /// <inheritdoc/>
         public void CancelDiscovery()
         {
-            // TODO: Cancel Discovery
-            // this.requestSender.CancelDiscovery();
+            this.requestSender.CancelDiscovery();
         }
 
         /// <inheritdoc/>
diff --git a/src/vstest.console/TestPlatformHelpers/TestRequestManager.cs b/src/vstest.console/TestPlatformHelpers/TestRequestManager.cs
index 109479fa63..3fcea2bf9b 100644
--- a/src/vstest.console/TestPlatformHelpers/TestRequestManager.cs
+++ b/src/vstest.console/TestPlatformHelpers/TestRequestManager.cs
@@ -36,21 +36,17 @@ namespace Microsoft.VisualStudio.TestPlatform.CommandLine.TestPlatformHelpers
     /// </summary>
     internal class TestRequestManager : ITestRequestManager
     {
-        private ITestPlatform testPlatform;
-
+        private readonly ITestPlatform testPlatform;
         private CommandLineOptions commandLineOptions;
-
-        private ITestPlatformEventSource testPlatformEventSource;
-
+        private readonly ITestPlatformEventSource testPlatformEventSource;
         private TestRunResultAggregator testRunResultAggregator;
-
         private static ITestRequestManager testRequestManagerInstance;
-
         private InferHelper inferHelper;
-
         private const int runRequestTimeout = 5000;
-
         private bool telemetryOptedIn;
+        private readonly object syncObject = new object();
+        private readonly Task<IMetricsPublisher> metricsPublisher;
+        private bool isDisposed;
 
         /// <summary>
         /// Maintains the current active execution request
@@ -58,11 +54,11 @@ internal class TestRequestManager : ITestRequestManager
         /// </summary>
         private ITestRunRequest currentTestRunRequest;
 
-        private object syncobject = new object();
-
-        private Task<IMetricsPublisher> metricsPublisher;
-
-        private bool isDisposed;
+        /// <summary>
+        /// Maintains the current active discovery request
+        /// Assumption : There can only be one active discovery request.
+        /// </summary>
+        private IDiscoveryRequest currentDiscoveryRequest;
 
         #region Constructor
 
@@ -161,36 +157,45 @@ public void DiscoverTests(DiscoveryRequestPayload discoveryPayload, ITestDiscove
             }
 
             // create discovery request
-            var criteria = new DiscoveryCriteria(discoveryPayload.Sources, batchSize, this.commandLineOptions.TestStatsEventTimeout, runsettings);
-            criteria.TestCaseFilter = this.commandLineOptions.TestCaseFilterValue;
+            var criteria = new DiscoveryCriteria(discoveryPayload.Sources, batchSize, this.commandLineOptions.TestStatsEventTimeout, runsettings)
+            {
+                TestCaseFilter = this.commandLineOptions.TestCaseFilterValue
+            };
 
-            try
+            // Make sure to run the run request inside a lock as the below section is not thread-safe
+            // There can be only one discovery or execution request at a given point in time
+            lock (this.syncObject)
             {
-                using (IDiscoveryRequest discoveryRequest = this.testPlatform.CreateDiscoveryRequest(requestData, criteria, discoveryPayload.TestPlatformOptions))
+                try
                 {
-                    try
-                    {
-                        discoveryEventsRegistrar?.RegisterDiscoveryEvents(discoveryRequest);
+                    EqtTrace.Info("TestRequestManager.DiscoverTests: Synchronization context taken");
 
-                        this.testPlatformEventSource.DiscoveryRequestStart();
+                    this.currentDiscoveryRequest = this.testPlatform.CreateDiscoveryRequest(requestData, criteria, discoveryPayload.TestPlatformOptions);
+                    discoveryEventsRegistrar?.RegisterDiscoveryEvents(this.currentDiscoveryRequest);
 
-                        discoveryRequest.DiscoverAsync();
-                        discoveryRequest.WaitForCompletion();
-                    }
+                    // Notify start of discovery start
+                    this.testPlatformEventSource.DiscoveryRequestStart();
 
-                    finally
+                    // Start the discovery of tests and wait for completion
+                    this.currentDiscoveryRequest.DiscoverAsync();
+                    this.currentDiscoveryRequest.WaitForCompletion();
+                }
+                finally
+                {
+                    if (this.currentDiscoveryRequest != null)
                     {
-                        discoveryEventsRegistrar?.UnregisterDiscoveryEvents(discoveryRequest);
+                        // Dispose the discovery request and unregister for events
+                        discoveryEventsRegistrar?.UnregisterDiscoveryEvents(currentDiscoveryRequest);
+                        this.currentDiscoveryRequest.Dispose();
+                        this.currentDiscoveryRequest = null;
                     }
-                }
-            }
-            finally
-            {
-                EqtTrace.Info("TestRequestManager.DiscoverTests: Discovery tests completed.");
-                this.testPlatformEventSource.DiscoveryRequestStop();
 
-                // Posts the Discovery Complete event.
-                this.metricsPublisher.Result.PublishMetrics(TelemetryDataConstants.TestDiscoveryCompleteEvent, requestData.MetricsCollection.Metrics);
+                    EqtTrace.Info("TestRequestManager.DiscoverTests: Discovery tests completed.");
+                    this.testPlatformEventSource.DiscoveryRequestStop();
+
+                    // Posts the Discovery Complete event.
+                    this.metricsPublisher.Result.PublishMetrics(TelemetryDataConstants.TestDiscoveryCompleteEvent, requestData.MetricsCollection.Metrics);
+                }
             }
         }
 
@@ -312,6 +317,15 @@ public void CancelTestRun()
             this.currentTestRunRequest?.CancelAsync();
         }
 
+        /// <summary>
+        /// Cancel the test discovery.
+        /// </summary>
+        public void CancelDiscovery()
+        {
+            EqtTrace.Info("TestRequestManager.CancelTestDiscovery: Sending cancel request.");
+            this.currentDiscoveryRequest?.Abort();
+        }
+
         /// <summary>
         /// Aborts the test run.
         /// </summary>
@@ -544,7 +558,7 @@ private void RunTests(IRequestData requestData, TestRunCriteria testRunCriteria,
             // TranslationLayer can process faster as it directly gets the raw unserialized messages whereas 
             // below logic needs to deserialize and do some cleanup
             // While this section is cleaning up, TranslationLayer can trigger run causing multiple threads to run the below section at the same time
-            lock (syncobject)
+            lock (this.syncObject)
             {
                 try
                 {
diff --git a/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DifferentTestFrameworkSimpleTests.cs b/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DifferentTestFrameworkSimpleTests.cs
index a58e5eec03..197c3eea23 100644
--- a/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DifferentTestFrameworkSimpleTests.cs
+++ b/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DifferentTestFrameworkSimpleTests.cs
@@ -122,7 +122,7 @@ public void RunTestsWithXunitAdapter(RunnerInfo runnerInfo)
         [NetFullTargetFrameworkDataSource]
         public void RunTestsWithChutzpahAdapter(RunnerInfo runnerInfo)
         {
-            AcceptanceTestBase.SetTestEnvironment(this.testEnvironment, runnerInfo);
+            SetTestEnvironment(this.testEnvironment, runnerInfo);
             this.Setup();
 
             var sources = new List<string>
@@ -147,16 +147,5 @@ public void RunTestsWithChutzpahAdapter(RunnerInfo runnerInfo)
             Assert.AreEqual(1, this.runEventHandler.TestResults.Count(t => t.Outcome == TestOutcome.Failed));
             Assert.AreEqual(1, testCase.FirstOrDefault().TestCase.LineNumber);
         }
-
-        private IList<string> GetTestAssemblies()
-        {
-            var testAssemblies = new List<string>
-                                     {
-                                         this.GetAssetFullPath("SimpleTestProject.dll"),
-                                         this.GetAssetFullPath("SimpleTestProject2.dll")
-                                     };
-
-            return testAssemblies;
-        }
     }
 }
\ No newline at end of file
diff --git a/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DiscoverTests.cs b/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DiscoverTests.cs
index ec852586ee..a274adf8bc 100644
--- a/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DiscoverTests.cs
+++ b/test/Microsoft.TestPlatform.AcceptanceTests/TranslationLayerTests/DiscoverTests.cs
@@ -3,15 +3,17 @@
 
 namespace Microsoft.TestPlatform.AcceptanceTests.TranslationLayerTests
 {
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
     using Microsoft.TestPlatform.TestUtilities;
     using Microsoft.TestPlatform.VsTestConsole.TranslationLayer.Interfaces;
     using Microsoft.VisualStudio.TestPlatform.Common.Telemetry;
+    using Microsoft.VisualStudio.TestPlatform.ObjectModel;
     using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client;
     using Microsoft.VisualStudio.TestTools.UnitTesting;
-    using System;
-    using System.Collections.Generic;
-    using System.Linq;
-    using VisualStudio.TestPlatform.ObjectModel.Logging;
+    using Moq;
 
     [TestClass]
     public class DiscoverTests : AcceptanceTestBase
@@ -169,6 +171,42 @@ public void DiscoverTestsUsingSourceNavigation(RunnerInfo runnerInfo)
             }
         }
 
+        [TestMethod]
+        [NetFullTargetFrameworkDataSource]
+        [NetCoreTargetFrameworkDataSource]
+        public void CancelTestDiscovery(RunnerInfo runnerInfo)
+        {
+            // Setup
+            var testAssemblies = new List<string>
+                                     {
+                                         this.GetAssetFullPath("DiscoveryTestProject.dll"),
+                                         this.GetAssetFullPath("SimpleTestProject.dll"),
+                                         this.GetAssetFullPath("SimpleTestProject2.dll")
+                                     };
+
+            SetTestEnvironment(this.testEnvironment, runnerInfo);
+            this.Setup();
+
+            var discoveredTests = new List<TestCase>();
+            var discoveryEvents = new Mock<ITestDiscoveryEventsHandler>();
+            discoveryEvents.Setup((events) => events.HandleDiscoveredTests(It.IsAny<IEnumerable<TestCase>>())).Callback
+                ((IEnumerable<TestCase> testcases) => { discoveredTests.AddRange(testcases); });
+
+            // Act
+            var discoveryTask = Task.Run(() =>
+            {
+                this.vstestConsoleWrapper.DiscoverTests(testAssemblies, this.GetDefaultRunSettings(), discoveryEvents.Object);
+            });
+
+            Task.Delay(2000).Wait();
+            vstestConsoleWrapper.CancelDiscovery();
+            discoveryTask.Wait();
+
+            // Assert.
+            int discoveredSources = discoveredTests.Select((testcase) => testcase.Source).Distinct().Count();
+            Assert.AreNotEqual(testAssemblies.Count, discoveredSources, "All test assemblies discovered");
+        }
+
         private IList<string> GetTestAssemblies()
         {
             var testAssemblies = new List<string>
diff --git a/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/Discovery/DiscovererEnumeratorTests.cs b/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/Discovery/DiscovererEnumeratorTests.cs
index d9ae243a93..cb56326c87 100644
--- a/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/Discovery/DiscovererEnumeratorTests.cs
+++ b/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/Discovery/DiscovererEnumeratorTests.cs
@@ -9,7 +9,7 @@ namespace TestPlatform.CrossPlatEngine.UnitTests.Discovery
     using System.Globalization;
     using System.Linq;
     using System.Reflection;
-
+    using System.Threading;
     using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework;
     using Microsoft.VisualStudio.TestPlatform.Common.Interfaces;
     using Microsoft.VisualStudio.TestPlatform.Common.Telemetry;
@@ -29,14 +29,15 @@ namespace TestPlatform.CrossPlatEngine.UnitTests.Discovery
     [TestClass]
     public class DiscovererEnumeratorTests
     {
-        private DiscovererEnumerator discovererEnumerator;
-        private Mock<ITestPlatformEventSource> mockTestPlatformEventSource;
-        private DiscoveryResultCache discoveryResultCache;
-        private Mock<IRequestData> mockRequestData;
-        private Mock<IMetricsCollection> mockMetricsCollection;
-        private Mock<IAssemblyProperties> mockAssemblyProperties;
-        private Mock<IRunSettings> runSettingsMock;
-        private Mock<IMessageLogger> messageLoggerMock;
+        private readonly CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
+        private readonly DiscovererEnumerator discovererEnumerator;
+        private readonly Mock<ITestPlatformEventSource> mockTestPlatformEventSource;
+        private readonly DiscoveryResultCache discoveryResultCache;
+        private readonly Mock<IRequestData> mockRequestData;
+        private readonly Mock<IMetricsCollection> mockMetricsCollection;
+        private readonly Mock<IAssemblyProperties> mockAssemblyProperties;
+        private readonly Mock<IRunSettings> runSettingsMock;
+        private readonly Mock<IMessageLogger> messageLoggerMock;
 
         public DiscovererEnumeratorTests()
         {
@@ -46,7 +47,7 @@ public DiscovererEnumeratorTests()
             this.mockMetricsCollection = new Mock<IMetricsCollection>();
             this.mockAssemblyProperties = new Mock<IAssemblyProperties>();
             this.mockRequestData.Setup(rd => rd.MetricsCollection).Returns(this.mockMetricsCollection.Object);
-            this.discovererEnumerator = new DiscovererEnumerator(this.mockRequestData.Object, this.discoveryResultCache, this.mockTestPlatformEventSource.Object, this.mockAssemblyProperties.Object);
+            this.discovererEnumerator = new DiscovererEnumerator(this.mockRequestData.Object, this.discoveryResultCache, this.mockTestPlatformEventSource.Object, this.mockAssemblyProperties.Object, this.cancellationTokenSource.Token);
             this.runSettingsMock = new Mock<IRunSettings>();
             this.messageLoggerMock = new Mock<IMessageLogger>();
             TestPluginCacheTests.SetupMockExtensions( new string[] { typeof(DiscovererEnumeratorTests).GetTypeInfo().Assembly.Location },
@@ -381,13 +382,50 @@ public void LoadTestsShouldCollectMetrics()
             mockMetricsCollector.Verify(rd => rd.Add(TelemetryDataConstants.TimeTakenToLoadAdaptersInSec, It.IsAny<object>()), Times.Once);
         }
 
+        [TestMethod]
+        public void LoadTestsShouldNotCallIntoDiscoverersWhenCancelled()
+        {
+            // Setup
+            string[] extensions = new string[] { typeof(DiscovererEnumeratorTests).GetTypeInfo().Assembly.Location };
+            TestPluginCacheTests.SetupMockExtensions(extensions, () => { });
+
+            var dllsources = new List<string>
+                              {
+                                  typeof(DiscoveryResultCacheTests).GetTypeInfo().Assembly.Location,
+                                  typeof(DiscoveryResultCacheTests).GetTypeInfo().Assembly.Location
+                              };
+            var jsonsources = new List<string>
+                              {
+                                  "test1.json",
+                                  "test2.json"
+                              };
+            var sources = new List<string>(dllsources);
+            sources.AddRange(jsonsources);
+
+            var extensionSourceMap = new Dictionary<string, IEnumerable<string>>
+            {
+                { "_none_", sources }
+            };
+
+            // Act
+            this.cancellationTokenSource.Cancel();
+            var runSettings = this.runSettingsMock.Object;
+            string testCaseFilter = "TestFilter";
+            this.discovererEnumerator.LoadTests(extensionSourceMap, runSettings, testCaseFilter, this.messageLoggerMock.Object);
+
+            // Validate
+            Assert.IsFalse(ManagedDllTestDiscoverer.IsManagedDiscoverTestCalled);
+            Assert.IsFalse(JsonTestDiscoverer.IsDiscoverTestCalled);
+            this.messageLoggerMock.Verify(logger => logger.SendMessage(TestMessageLevel.Warning, "Discovery of tests cancelled."), Times.Once);
+        }
+
         [TestMethod]
         public void LoadTestsShouldCallIntoTheAdapterWithTheRightTestCaseSink()
         {
-             this.InvokeLoadTestWithMockSetup();
+            this.InvokeLoadTestWithMockSetup();
 
-             Assert.IsTrue(ManagedDllTestDiscoverer.IsManagedDiscoverTestCalled);
-             Assert.AreEqual(2, this.discoveryResultCache.Tests.Count);
+            Assert.IsTrue(ManagedDllTestDiscoverer.IsManagedDiscoverTestCalled);
+            Assert.AreEqual(2, this.discoveryResultCache.Tests.Count);
         }
 
         [TestMethod]
@@ -483,7 +521,7 @@ public void LoadTestsShouldLogWarningMessageOnNoTestsInAssemblies()
             var expectedMessage =
                 $"No test is available in {sourcesString}. Make sure that test discoverer & executors are registered and platform & framework version settings are appropriate and try again.";
 
-            this.messageLoggerMock.Verify( l => l.SendMessage(TestMessageLevel.Warning, expectedMessage));
+            this.messageLoggerMock.Verify(l => l.SendMessage(TestMessageLevel.Warning, expectedMessage));
         }
 
         [TestMethod]
diff --git a/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/EventHandlers/TestRequestHandlerTests.cs b/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/EventHandlers/TestRequestHandlerTests.cs
index d728a07d4e..912aa8ee75 100644
--- a/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/EventHandlers/TestRequestHandlerTests.cs
+++ b/test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/EventHandlers/TestRequestHandlerTests.cs
@@ -131,7 +131,7 @@ public void ProcessRequestsShouldProcessMessagesUntilSessionCompleted()
             var task = this.ProcessRequestsAsync(this.mockTestHostManagerFactory.Object);
 
             this.SendSessionEnd();
-            Assert.IsTrue(task.Wait(20));
+            Assert.IsTrue(task.Wait(2000));
         }
 
         #region Version Check Protocol
diff --git a/test/TestAssets/DiscoveryTestProject/DiscoveryTestProject.csproj b/test/TestAssets/DiscoveryTestProject/DiscoveryTestProject.csproj
new file mode 100644
index 0000000000..36b0a05122
--- /dev/null
+++ b/test/TestAssets/DiscoveryTestProject/DiscoveryTestProject.csproj
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <!-- Imports Common TestAssets props. -->
+  <Import Project="..\..\..\scripts\build\TestAssets.props" />
+  <Import Project="..\..\..\scripts\build\TestPlatform.Dependencies.props" />
+  <!-- Package dependency versions -->
+
+  <PropertyGroup>
+    <AssemblyName>DiscoveryTestProject</AssemblyName>
+    <TargetFrameworks>netcoreapp1.0;netcoreapp1.1;netcoreapp2.0;net451</TargetFrameworks>
+    <PlatformTarget>x64</PlatformTarget>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="MSTest.TestFramework">
+      <Version>$(MSTestFrameworkVersion)</Version>
+    </PackageReference>
+    <PackageReference Include="MSTest.TestAdapter">
+      <Version>$(MSTestAdapterVersion)</Version>
+    </PackageReference>
+    <PackageReference Include="Microsoft.NET.Test.Sdk">
+      <Version>$(NETTestSdkPreviousVersion)</Version>
+    </PackageReference>
+  </ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net451' ">
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Windows.Forms" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
+  </ItemGroup>
+</Project>
diff --git a/test/TestAssets/DiscoveryTestProject/LongDiscoveryTestClass.cs b/test/TestAssets/DiscoveryTestProject/LongDiscoveryTestClass.cs
new file mode 100644
index 0000000000..2d5c65feeb
--- /dev/null
+++ b/test/TestAssets/DiscoveryTestProject/LongDiscoveryTestClass.cs
@@ -0,0 +1,26 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+
+namespace DiscoveryTestProject3
+{
+    [TestClass]
+    public class LongDiscoveryTestClass
+    {
+        [MyTestMethod]
+        public void CustomTestMethod()
+        {
+
+        }
+    }
+
+    internal class MyTestMethodAttribute : TestMethodAttribute
+    {
+        public MyTestMethodAttribute()
+        {
+            Thread.Sleep(10000);
+        }
+    }
+}