diff --git a/src/Microsoft.TestPlatform.Client/AttachmentsProcessing/TestRunAttachmentsProcessingEventsHandler.cs b/src/Microsoft.TestPlatform.Client/AttachmentsProcessing/TestRunAttachmentsProcessingEventsHandler.cs
index 0d15cc77cd..be4cc1b76c 100644
--- a/src/Microsoft.TestPlatform.Client/AttachmentsProcessing/TestRunAttachmentsProcessingEventsHandler.cs
+++ b/src/Microsoft.TestPlatform.Client/AttachmentsProcessing/TestRunAttachmentsProcessingEventsHandler.cs
@@ -9,14 +9,12 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing;
 
 /// <summary>
 /// The test run attachments processing events handler.
 /// </summary>
-/// 
+///
 public class TestRunAttachmentsProcessingEventsHandler : ITestRunAttachmentsProcessingEventsHandler
 {
     private readonly ICommunicationManager _communicationManager;
@@ -35,7 +33,7 @@ public void HandleTestRunAttachmentsProcessingComplete(TestRunAttachmentsProcess
     {
         EqtTrace.Info("Test run attachments processing completed.");
 
-        var payload = new TestRunAttachmentsProcessingCompletePayload()
+        var payload = new TestRunAttachmentsProcessingCompletePayload
         {
             AttachmentsProcessingCompleteEventArgs = attachmentsProcessingCompleteEventArgs,
             Attachments = lastChunk
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
index a058416caa..d965c51b91 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Net;
 using System.Threading;
@@ -26,8 +27,6 @@
 
 using CommunicationUtilitiesResources = Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Resources.Resources;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 
 /// <summary>
@@ -45,9 +44,9 @@ public class DesignModeClient : IDesignModeClient
     private readonly TestSessionMessageLogger _testSessionMessageLogger;
     private readonly object _lockObject = new();
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
-    protected Action<Message> onCustomTestHostLaunchAckReceived;
+    protected Action<Message>? onCustomTestHostLaunchAckReceived;
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
-    protected Action<Message> onAttachDebuggerAckRecieved;
+    protected Action<Message>? onAttachDebuggerAckRecieved;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="DesignModeClient"/> class.
@@ -81,11 +80,12 @@ internal DesignModeClient(ICommunicationManager communicationManager, IDataSeria
     /// <summary>
     /// Property exposing the Instance
     /// </summary>
-    public static IDesignModeClient Instance { get; private set; }
+    public static IDesignModeClient? Instance { get; private set; }
 
     /// <summary>
     /// Initializes DesignMode
     /// </summary>
+    [MemberNotNull(nameof(Instance))]
     public static void Initialize()
     {
         Instance = new DesignModeClient();
@@ -102,7 +102,7 @@ public static void Initialize()
     /// </param>
     public void ConnectToClientAndProcessRequests(int port, ITestRequestManager testRequestManager)
     {
-        EqtTrace.Info("Trying to connect to server on port : {0}", port);
+        EqtTrace.Info("Trying to connect to server on port: {0}", port);
         _communicationManager.SetupClientAsync(new IPEndPoint(IPAddress.Loopback, port));
 
         var connectionTimeoutInSecs = EnvironmentHelper.GetConnectionTimeout();
@@ -115,7 +115,7 @@ public void ConnectToClientAndProcessRequests(int port, ITestRequestManager test
         }
         else
         {
-            EqtTrace.Error("DesignModeClient : ConnectToClientAndProcessRequests : Client timed out while connecting to the server.");
+            EqtTrace.Error("DesignModeClient.ConnectToClientAndProcessRequests: Client timed out while connecting to the server.");
             Dispose();
             throw new TimeoutException(
                 string.Format(
@@ -135,7 +135,7 @@ public void HandleParentProcessExit()
         // this should end the "ProcessRequests" loop with an exception
         Dispose();
 
-        EqtTrace.Info("DesignModeClient: Parent process exited, Exiting myself..");
+        EqtTrace.Info("DesignModeClient.HandleParentProcessExit: Parent process exited, Exiting myself...");
 
         _platformEnvironment.Exit(1);
     }
@@ -303,7 +303,7 @@ public int LaunchCustomHost(TestProcessStartInfo testProcessStartInfo, Cancellat
         lock (_lockObject)
         {
             var waitHandle = new AutoResetEvent(false);
-            Message ackMessage = null;
+            Message? ackMessage = null;
             onCustomTestHostLaunchAckReceived = (ackRawMessage) =>
             {
                 ackMessage = ackRawMessage;
@@ -343,7 +343,7 @@ public bool AttachDebuggerToProcess(AttachDebuggerInfo attachDebuggerInfo, Cance
         lock (_lockObject)
         {
             var waitHandle = new AutoResetEvent(false);
-            Message ackMessage = null;
+            Message? ackMessage = null;
             onAttachDebuggerAckRecieved = (ackRawMessage) =>
             {
                 ackMessage = ackRawMessage;
@@ -363,7 +363,7 @@ public bool AttachDebuggerToProcess(AttachDebuggerInfo attachDebuggerInfo, Cance
             {
                 var payload = new EditorAttachDebuggerPayload
                 {
-                    TargetFramework = attachDebuggerInfo.TargetFramework.ToString(),
+                    TargetFramework = attachDebuggerInfo.TargetFramework?.ToString(),
                     ProcessID = attachDebuggerInfo.ProcessId,
                 };
                 _communicationManager.SendMessage(MessageType.EditorAttachDebugger2, payload);
@@ -394,7 +394,7 @@ public void SendRawMessage(string rawMessage)
     }
 
     /// <inheritdoc />
-    public void SendTestMessage(TestMessageLevel level, string message)
+    public void SendTestMessage(TestMessageLevel level, string? message)
     {
         var payload = new TestMessagePayload { MessageLevel = level, Message = message };
         _communicationManager.SendMessage(MessageType.TestMessage, payload);
@@ -405,7 +405,7 @@ public void SendTestMessage(TestMessageLevel level, string message)
     /// </summary>
     /// <param name="sender"></param>
     /// <param name="e"></param>
-    public void TestRunMessageHandler(object sender, TestRunMessageEventArgs e)
+    public void TestRunMessageHandler(object? sender, TestRunMessageEventArgs e)
     {
         // save into trace log and send the message to the IDE
         //
@@ -440,41 +440,40 @@ public void TestRunMessageHandler(object sender, TestRunMessageEventArgs e)
 
     private void StartTestRun(TestRunRequestPayload testRunPayload, ITestRequestManager testRequestManager, bool shouldLaunchTesthost)
     {
-        Task.Run(
-            () =>
+        Task.Run(() =>
+        {
+            try
             {
-                try
-                {
-                    testRequestManager.ResetOptions();
+                testRequestManager.ResetOptions();
+
+                // We must avoid re-launching the test host if the test run payload already
+                // contains test session info. Test session info being present is an indicative
+                // of an already running test host spawned by a start test session call.
+                var customLauncher =
+                    shouldLaunchTesthost && testRunPayload.TestSessionInfo == null
+                        ? DesignModeTestHostLauncherFactory.GetCustomHostLauncherForTestRun(
+                            this,
+                            testRunPayload.DebuggingEnabled)
+                        : null;
+
+                testRequestManager.RunTests(testRunPayload, customLauncher, new DesignModeTestEventsRegistrar(this), _protocolConfig);
+            }
+            catch (Exception ex)
+            {
+                EqtTrace.Error("DesignModeClient: Exception in StartTestRun: " + ex);
 
-                    // We must avoid re-launching the test host if the test run payload already
-                    // contains test session info. Test session info being present is an indicative
-                    // of an already running test host spawned by a start test session call.
-                    var customLauncher =
-                        shouldLaunchTesthost && testRunPayload.TestSessionInfo == null
-                            ? DesignModeTestHostLauncherFactory.GetCustomHostLauncherForTestRun(
-                                this,
-                                testRunPayload.DebuggingEnabled)
-                            : null;
-
-                    testRequestManager.RunTests(testRunPayload, customLauncher, new DesignModeTestEventsRegistrar(this), _protocolConfig);
-                }
-                catch (Exception ex)
+                var testMessagePayload = new TestMessagePayload { MessageLevel = TestMessageLevel.Error, Message = ex.ToString() };
+                _communicationManager.SendMessage(MessageType.TestMessage, testMessagePayload);
+                var runCompletePayload = new TestRunCompletePayload()
                 {
-                    EqtTrace.Error("DesignModeClient: Exception in StartTestRun: " + ex);
-
-                    var testMessagePayload = new TestMessagePayload { MessageLevel = TestMessageLevel.Error, Message = ex.ToString() };
-                    _communicationManager.SendMessage(MessageType.TestMessage, testMessagePayload);
-                    var runCompletePayload = new TestRunCompletePayload()
-                    {
-                        TestRunCompleteArgs = new TestRunCompleteEventArgs(null, false, true, ex, null, null, TimeSpan.MinValue),
-                        LastRunTests = null
-                    };
+                    TestRunCompleteArgs = new TestRunCompleteEventArgs(null, false, true, ex, null, null, TimeSpan.MinValue),
+                    LastRunTests = null
+                };
 
-                    // Send run complete to translation layer
-                    _communicationManager.SendMessage(MessageType.ExecutionComplete, runCompletePayload);
-                }
-            });
+                // Send run complete to translation layer
+                _communicationManager.SendMessage(MessageType.ExecutionComplete, runCompletePayload);
+            }
+        });
     }
 
     private void StartDiscovery(DiscoveryRequestPayload discoveryRequestPayload, ITestRequestManager testRequestManager)
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestEventsRegistrar.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestEventsRegistrar.cs
index cecf859a19..f945491853 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestEventsRegistrar.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestEventsRegistrar.cs
@@ -2,13 +2,9 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using Microsoft.VisualStudio.TestPlatform.Common.Interfaces;
-
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client;
-
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 
 /// <summary>
@@ -62,7 +58,7 @@ private void OnRawMessageReceived(object sender, string rawMessage)
         _designModeClient.SendRawMessage(rawMessage);
     }
 
-    public void LogWarning(string message)
+    public void LogWarning(string? message)
     {
         _designModeClient.SendTestMessage(TestMessageLevel.Warning, message);
     }
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncher.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncher.cs
index 03f02a471c..73df6ca0f6 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncher.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncher.cs
@@ -7,8 +7,6 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 
 /// <summary>
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncherFactory.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncherFactory.cs
index f1f56342d9..67400d6b18 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncherFactory.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeTestHostLauncherFactory.cs
@@ -3,8 +3,6 @@
 
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 
 /// <summary>
@@ -12,8 +10,8 @@ namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 /// </summary>
 public static class DesignModeTestHostLauncherFactory
 {
-    private static ITestHostLauncher3 s_defaultLauncher;
-    private static ITestHostLauncher3 s_debugLauncher;
+    private static ITestHostLauncher3? s_defaultLauncher;
+    private static ITestHostLauncher3? s_debugLauncher;
 
     public static ITestHostLauncher3 GetCustomHostLauncherForTestRun(IDesignModeClient designModeClient, bool debuggingEnabled)
     {
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/IDesignModeClient.cs b/src/Microsoft.TestPlatform.Client/DesignMode/IDesignModeClient.cs
index 6b13c4e6f2..169a6decee 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/IDesignModeClient.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/IDesignModeClient.cs
@@ -9,8 +9,6 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.DesignMode;
 
 /// <summary>
@@ -56,5 +54,5 @@ public interface IDesignModeClient : IDisposable
     /// </summary>
     /// <param name="level">Level for the message</param>
     /// <param name="message">Actual message string</param>
-    void SendTestMessage(TestMessageLevel level, string message);
+    void SendTestMessage(TestMessageLevel level, string? message);
 }
diff --git a/src/Microsoft.TestPlatform.Client/Discovery/DiscoveryRequest.cs b/src/Microsoft.TestPlatform.Client/Discovery/DiscoveryRequest.cs
index 7f71a70d09..d2866e204c 100644
--- a/src/Microsoft.TestPlatform.Client/Discovery/DiscoveryRequest.cs
+++ b/src/Microsoft.TestPlatform.Client/Discovery/DiscoveryRequest.cs
@@ -18,8 +18,6 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
 using Microsoft.VisualStudio.TestPlatform.Utilities;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.Discovery;
 
 /// <summary>
@@ -164,30 +162,30 @@ bool IRequest.WaitForCompletion(int timeout)
     /// <summary>
     /// Raised when the test discovery starts.
     /// </summary>
-    public event EventHandler<DiscoveryStartEventArgs> OnDiscoveryStart;
+    public event EventHandler<DiscoveryStartEventArgs>? OnDiscoveryStart;
 
     /// <summary>
     /// Raised when the test discovery completes.
     /// </summary>
-    public event EventHandler<DiscoveryCompleteEventArgs> OnDiscoveryComplete;
+    public event EventHandler<DiscoveryCompleteEventArgs>? OnDiscoveryComplete;
 
     /// <summary>
     /// Raised when the message is received.
     /// </summary>
     /// <remarks>TestRunMessageEventArgs should be renamed to more generic</remarks>
-    public event EventHandler<TestRunMessageEventArgs> OnDiscoveryMessage;
+    public event EventHandler<TestRunMessageEventArgs>? OnDiscoveryMessage;
 
     /// <summary>
     /// Raised when new tests are discovered in this discovery request.
     /// </summary>
-    public event EventHandler<DiscoveredTestsEventArgs> OnDiscoveredTests;
+    public event EventHandler<DiscoveredTestsEventArgs>? OnDiscoveredTests;
 
     /// <summary>
     ///  Raised when a discovery event related message is received from host
     ///  This is required if one wants to re-direct the message over the process boundary without any processing overhead
     ///  All the discovery events should come as raw messages as well as proper serialized events like OnDiscoveredTests
     /// </summary>
-    public event EventHandler<string> OnRawMessageReceived;
+    public event EventHandler<string>? OnRawMessageReceived;
 
     /// <summary>
     /// Specifies the discovery criterion
@@ -217,7 +215,7 @@ public DiscoveryCriteria DiscoveryCriteria
     #region ITestDiscoveryEventsHandler2 Methods
 
     /// <inheritdoc/>
-    public void HandleDiscoveryComplete(DiscoveryCompleteEventArgs discoveryCompleteEventArgs, IEnumerable<TestCase> lastChunk)
+    public void HandleDiscoveryComplete(DiscoveryCompleteEventArgs discoveryCompleteEventArgs, IEnumerable<TestCase>? lastChunk)
     {
         EqtTrace.Verbose("DiscoveryRequest.HandleDiscoveryComplete: Begin processing discovery complete notification. Aborted: {0}, TotalTests: {1}", discoveryCompleteEventArgs.IsAborted, discoveryCompleteEventArgs.TotalCount);
 
@@ -307,7 +305,7 @@ public void HandleDiscoveryComplete(DiscoveryCompleteEventArgs discoveryComplete
     }
 
     /// <inheritdoc/>
-    public void HandleDiscoveredTests(IEnumerable<TestCase> discoveredTestCases)
+    public void HandleDiscoveredTests(IEnumerable<TestCase>? discoveredTestCases)
     {
         EqtTrace.Verbose("DiscoveryRequest.HandleDiscoveredTests: Starting.");
 
@@ -402,66 +400,68 @@ private void HandleLoggerManagerDiscoveryComplete(DiscoveryCompletePayload disco
     /// <param name="discoveryCompletePayload">Discovery complete payload.</param>
     /// <param name="message">Message.</param>
     /// <returns>Updated rawMessage.</returns>
-    private string UpdateRawMessageWithTelemetryInfo(DiscoveryCompletePayload discoveryCompletePayload, Message message)
+    private string? UpdateRawMessageWithTelemetryInfo(DiscoveryCompletePayload? discoveryCompletePayload, Message? message)
     {
         var rawMessage = default(string);
 
-        if (RequestData.IsTelemetryOptedIn)
+        if (!RequestData.IsTelemetryOptedIn)
         {
-            if (discoveryCompletePayload != null)
-            {
-                if (discoveryCompletePayload.Metrics == null)
-                {
-                    discoveryCompletePayload.Metrics = RequestData.MetricsCollection.Metrics;
-                }
-                else
-                {
-                    foreach (var kvp in RequestData.MetricsCollection.Metrics)
-                    {
-                        discoveryCompletePayload.Metrics[kvp.Key] = kvp.Value;
-                    }
-                }
-
-                var discoveryFinalTimeTakenForDesignMode = DateTime.UtcNow - _discoveryStartTime;
-
-                // Collecting Total Time Taken
-                discoveryCompletePayload.Metrics[TelemetryDataConstants.TimeTakenInSecForDiscovery] = discoveryFinalTimeTakenForDesignMode.TotalSeconds;
-
-                // Add extensions discovered by vstest.console.
-                //
-                // TODO(copoiena):
-                // Doing extension merging here is incorrect because we can end up not merging the
-                // cached extensions for the current process (i.e. vstest.console) and hence have
-                // an incomplete list of discovered extensions. This can happen because this method
-                // is called only if telemetry is opted in (see: HandleRawMessage). We should handle
-                // this merge a level above in order to be consistent, but that means we'd have to
-                // deserialize all raw messages no matter if telemetry is opted in or not and that
-                // would probably mean a performance hit.
-                discoveryCompletePayload.DiscoveredExtensions = TestExtensions.CreateMergedDictionary(
-                    discoveryCompletePayload.DiscoveredExtensions,
-                    TestPluginCache.Instance.TestExtensions?.GetCachedExtensions());
-
-                // Write extensions to telemetry data.
-                TestExtensions.AddExtensionTelemetry(
-                    discoveryCompletePayload.Metrics,
-                    discoveryCompletePayload.DiscoveredExtensions);
-            }
+            return rawMessage;
+        }
 
-            if (message is VersionedMessage message1)
+        if (discoveryCompletePayload != null)
+        {
+            if (discoveryCompletePayload.Metrics == null)
             {
-                var version = message1.Version;
-
-                rawMessage = _dataSerializer.SerializePayload(
-                    MessageType.DiscoveryComplete,
-                    discoveryCompletePayload,
-                    version);
+                discoveryCompletePayload.Metrics = RequestData.MetricsCollection.Metrics;
             }
             else
             {
-                rawMessage = _dataSerializer.SerializePayload(
-                    MessageType.DiscoveryComplete,
-                    discoveryCompletePayload);
+                foreach (var kvp in RequestData.MetricsCollection.Metrics)
+                {
+                    discoveryCompletePayload.Metrics[kvp.Key] = kvp.Value;
+                }
             }
+
+            var discoveryFinalTimeTakenForDesignMode = DateTime.UtcNow - _discoveryStartTime;
+
+            // Collecting Total Time Taken
+            discoveryCompletePayload.Metrics[TelemetryDataConstants.TimeTakenInSecForDiscovery] = discoveryFinalTimeTakenForDesignMode.TotalSeconds;
+
+            // Add extensions discovered by vstest.console.
+            //
+            // TODO(copoiena):
+            // Doing extension merging here is incorrect because we can end up not merging the
+            // cached extensions for the current process (i.e. vstest.console) and hence have
+            // an incomplete list of discovered extensions. This can happen because this method
+            // is called only if telemetry is opted in (see: HandleRawMessage). We should handle
+            // this merge a level above in order to be consistent, but that means we'd have to
+            // deserialize all raw messages no matter if telemetry is opted in or not and that
+            // would probably mean a performance hit.
+            discoveryCompletePayload.DiscoveredExtensions = TestExtensions.CreateMergedDictionary(
+                discoveryCompletePayload.DiscoveredExtensions,
+                TestPluginCache.Instance.TestExtensions?.GetCachedExtensions());
+
+            // Write extensions to telemetry data.
+            TestExtensions.AddExtensionTelemetry(
+                discoveryCompletePayload.Metrics,
+                discoveryCompletePayload.DiscoveredExtensions);
+        }
+
+        if (message is VersionedMessage message1)
+        {
+            var version = message1.Version;
+
+            rawMessage = _dataSerializer.SerializePayload(
+                MessageType.DiscoveryComplete,
+                discoveryCompletePayload,
+                version);
+        }
+        else
+        {
+            rawMessage = _dataSerializer.SerializePayload(
+                MessageType.DiscoveryComplete,
+                discoveryCompletePayload);
         }
 
         return rawMessage;
@@ -499,7 +499,7 @@ private void Dispose(bool disposing)
                 }
 
                 // Indicate that object has been disposed
-                _discoveryCompleted = null;
+                _discoveryCompleted = null!;
                 _disposed = true;
             }
         }
diff --git a/src/Microsoft.TestPlatform.Client/Execution/TestRunRequest.cs b/src/Microsoft.TestPlatform.Client/Execution/TestRunRequest.cs
index e91b440ee1..3177f9b0fd 100644
--- a/src/Microsoft.TestPlatform.Client/Execution/TestRunRequest.cs
+++ b/src/Microsoft.TestPlatform.Client/Execution/TestRunRequest.cs
@@ -8,6 +8,7 @@
 using System.Linq;
 using System.Threading;
 
+using Microsoft.VisualStudio.TestPlatform.Common;
 using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework;
 using Microsoft.VisualStudio.TestPlatform.Common.ExtensionFramework.Utilities;
 using Microsoft.VisualStudio.TestPlatform.Common.Telemetry;
@@ -24,8 +25,6 @@
 
 using ClientResources = Microsoft.VisualStudio.TestPlatform.Client.Resources.Resources;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.Execution;
 
 public class TestRunRequest : ITestRunRequest, IInternalTestRunEventsHandler
@@ -53,7 +52,7 @@ public class TestRunRequest : ITestRunRequest, IInternalTestRunEventsHandler
     /// <summary>
     /// Tracks the time taken by each run request
     /// </summary>
-    private Stopwatch _runRequestTimeTracker;
+    private Stopwatch? _runRequestTimeTracker;
 
     private readonly IDataSerializer _dataSerializer;
 
@@ -62,7 +61,7 @@ public class TestRunRequest : ITestRunRequest, IInternalTestRunEventsHandler
     /// </summary>
     private long _testSessionTimeout;
 
-    private Timer _timer;
+    private Timer? _timer;
 
     /// <summary>
     /// Execution Start Time
@@ -81,10 +80,10 @@ internal TestRunRequest(IRequestData requestData, TestRunCriteria testRunCriteri
 
     internal TestRunRequest(IRequestData requestData, TestRunCriteria testRunCriteria, IProxyExecutionManager executionManager, ITestLoggerManager loggerManager, IDataSerializer dataSerializer)
     {
-        Debug.Assert(testRunCriteria != null, "Test run criteria cannot be null");
-        Debug.Assert(executionManager != null, "ExecutionManager cannot be null");
-        Debug.Assert(requestData != null, "request Data is null");
-        Debug.Assert(loggerManager != null, "LoggerManager cannot be null");
+        TPDebug.Assert(testRunCriteria != null, "Test run criteria cannot be null");
+        TPDebug.Assert(executionManager != null, "ExecutionManager cannot be null");
+        TPDebug.Assert(requestData != null, "request Data is null");
+        TPDebug.Assert(loggerManager != null, "LoggerManager cannot be null");
 
         EqtTrace.Verbose("TestRunRequest.ExecuteAsync: Creating test run request.");
 
@@ -168,7 +167,7 @@ public int ExecuteAsync()
         }
     }
 
-    internal void OnTestSessionTimeout(object obj)
+    internal void OnTestSessionTimeout(object? obj)
     {
         EqtTrace.Verbose("TestRunRequest.OnTestSessionTimeout: calling cancellation as test run exceeded testSessionTimeout {0} milliseconds", _testSessionTimeout);
 
@@ -282,30 +281,30 @@ public ITestRunConfiguration TestRunConfiguration
     /// <summary>
     /// Raised when the test run statistics change.
     /// </summary>
-    public event EventHandler<TestRunChangedEventArgs> OnRunStatsChange;
+    public event EventHandler<TestRunChangedEventArgs>? OnRunStatsChange;
 
     /// <summary>
     /// Raised when the test run starts.
     /// </summary>
-    public event EventHandler<TestRunStartEventArgs> OnRunStart;
+    public event EventHandler<TestRunStartEventArgs>? OnRunStart;
 
     /// <summary>
     /// Raised when the test message is received.
     /// </summary>
-    public event EventHandler<TestRunMessageEventArgs> TestRunMessage;
+    public event EventHandler<TestRunMessageEventArgs>? TestRunMessage;
 
 
     /// <summary>
     /// Raised when the test run completes.
     /// </summary>
-    public event EventHandler<TestRunCompleteEventArgs> OnRunCompletion;
+    public event EventHandler<TestRunCompleteEventArgs>? OnRunCompletion;
 
 
     /// <summary>
     /// Raised when data collection message is received.
     /// </summary>
 #pragma warning disable 67
-    public event EventHandler<DataCollectionMessageEventArgs> DataCollectionMessage;
+    public event EventHandler<DataCollectionMessageEventArgs>? DataCollectionMessage;
 #pragma warning restore 67
 
     /// <summary>
@@ -313,7 +312,7 @@ public ITestRunConfiguration TestRunConfiguration
     ///  This is required if one wants to re-direct the message over the process boundary without any processing overhead
     ///  All the run events should come as raw messages as well as proper serialized events like OnRunStatsChange
     /// </summary>
-    public event EventHandler<string> OnRawMessageReceived;
+    public event EventHandler<string>? OnRawMessageReceived;
 
     /// <summary>
     /// Parent execution manager
@@ -355,7 +354,7 @@ public void Dispose()
     /// <summary>
     /// Invoked when test run is complete
     /// </summary>
-    public void HandleTestRunComplete(TestRunCompleteEventArgs runCompleteArgs, TestRunChangedEventArgs lastChunkArgs, ICollection<AttachmentSet> runContextAttachments, ICollection<string> executorUris)
+    public void HandleTestRunComplete(TestRunCompleteEventArgs runCompleteArgs, TestRunChangedEventArgs? lastChunkArgs, ICollection<AttachmentSet>? runContextAttachments, ICollection<string>? executorUris)
     {
         ValidateArg.NotNull(runCompleteArgs, nameof(runCompleteArgs));
 
@@ -384,7 +383,7 @@ public void HandleTestRunComplete(TestRunCompleteEventArgs runCompleteArgs, Test
 
             try
             {
-                _runRequestTimeTracker.Stop();
+                _runRequestTimeTracker?.Stop();
 
                 if (lastChunkArgs != null)
                 {
@@ -402,7 +401,7 @@ public void HandleTestRunComplete(TestRunCompleteEventArgs runCompleteArgs, Test
                         // This is required as TMI adapter is sending attachments as List which cannot be type casted to Collection.
                         runContextAttachments != null ? new Collection<AttachmentSet>(runContextAttachments.ToList()) : null,
                         runCompleteArgs.InvokedDataCollectors,
-                        _runRequestTimeTracker.Elapsed);
+                        _runRequestTimeTracker!.Elapsed);
 
                 // Add extensions discovered by vstest.console.
                 //
@@ -463,40 +462,42 @@ public void HandleTestRunComplete(TestRunCompleteEventArgs runCompleteArgs, Test
     /// <summary>
     /// Invoked when test run statistics change.
     /// </summary>
-    public virtual void HandleTestRunStatsChange(TestRunChangedEventArgs testRunChangedArgs)
+    public virtual void HandleTestRunStatsChange(TestRunChangedEventArgs? testRunChangedArgs)
     {
-        if (testRunChangedArgs != null)
+        if (testRunChangedArgs == null)
+        {
+            return;
+        }
+
+        EqtTrace.Verbose("TestRunRequest:SendTestRunStatsChange: Starting.");
+        if (testRunChangedArgs.ActiveTests != null)
         {
-            EqtTrace.Verbose("TestRunRequest:SendTestRunStatsChange: Starting.");
-            if (testRunChangedArgs.ActiveTests != null)
+            // Do verbose check to save performance in iterating test cases
+            if (EqtTrace.IsVerboseEnabled)
             {
-                // Do verbose check to save performance in iterating test cases
-                if (EqtTrace.IsVerboseEnabled)
+                foreach (TestCase testCase in testRunChangedArgs.ActiveTests)
                 {
-                    foreach (TestCase testCase in testRunChangedArgs.ActiveTests)
-                    {
-                        EqtTrace.Verbose("InProgress is {0}", testCase.DisplayName);
-                    }
+                    EqtTrace.Verbose("InProgress is {0}", testCase.DisplayName);
                 }
             }
+        }
 
-            lock (_syncObject)
+        lock (_syncObject)
+        {
+            // If this object is disposed, don't do anything
+            if (_disposed)
             {
-                // If this object is disposed, don't do anything
-                if (_disposed)
-                {
-                    EqtTrace.Warning("TestRunRequest.SendTestRunStatsChange: Ignoring as the object is disposed.");
-                    return;
-                }
-
-                // TODO: Invoke this event in a separate thread.
-                // For now, I am setting the ConcurrencyMode on the callback attribute to Multiple
-                LoggerManager.HandleTestRunStatsChange(testRunChangedArgs);
-                OnRunStatsChange.SafeInvoke(this, testRunChangedArgs, "TestRun.RunStatsChanged");
+                EqtTrace.Warning("TestRunRequest.SendTestRunStatsChange: Ignoring as the object is disposed.");
+                return;
             }
 
-            EqtTrace.Info("TestRunRequest:SendTestRunStatsChange: Completed.");
+            // TODO: Invoke this event in a separate thread.
+            // For now, I am setting the ConcurrencyMode on the callback attribute to Multiple
+            LoggerManager.HandleTestRunStatsChange(testRunChangedArgs);
+            OnRunStatsChange.SafeInvoke(this, testRunChangedArgs, "TestRun.RunStatsChanged");
         }
+
+        EqtTrace.Info("TestRunRequest:SendTestRunStatsChange: Completed.");
     }
 
     /// <summary>
@@ -550,28 +551,30 @@ public void HandleRawMessage(string rawMessage)
     /// <param name="testRunCompletePayload">TestRun complete payload.</param>
     private void HandleLoggerManagerTestRunComplete(TestRunCompletePayload testRunCompletePayload)
     {
-        if (LoggerManager.LoggersInitialized && testRunCompletePayload != null)
+        if (!LoggerManager.LoggersInitialized || testRunCompletePayload == null)
         {
-            // Send last chunk to logger manager.
-            if (testRunCompletePayload.LastRunTests != null)
-            {
-                LoggerManager.HandleTestRunStatsChange(testRunCompletePayload.LastRunTests);
-            }
+            return;
+        }
 
-            // Note: In HandleRawMessage attachments are considered from TestRunCompleteArgs, while in HandleTestRunComplete attachments are considered directly from testRunCompletePayload.
-            // Ideally we should have attachmentSets at one place only.
-            // Send test run complete to logger manager.
-            TestRunCompleteEventArgs testRunCompleteArgs =
-                new(
-                    testRunCompletePayload.TestRunCompleteArgs.TestRunStatistics,
-                    testRunCompletePayload.TestRunCompleteArgs.IsCanceled,
-                    testRunCompletePayload.TestRunCompleteArgs.IsAborted,
-                    testRunCompletePayload.TestRunCompleteArgs.Error,
-                    testRunCompletePayload.TestRunCompleteArgs.AttachmentSets,
-                    testRunCompletePayload.TestRunCompleteArgs.InvokedDataCollectors,
-                    _runRequestTimeTracker.Elapsed);
-            LoggerManager.HandleTestRunComplete(testRunCompleteArgs);
+        // Send last chunk to logger manager.
+        if (testRunCompletePayload.LastRunTests != null)
+        {
+            LoggerManager.HandleTestRunStatsChange(testRunCompletePayload.LastRunTests);
         }
+
+        // Note: In HandleRawMessage attachments are considered from TestRunCompleteArgs, while in HandleTestRunComplete attachments are considered directly from testRunCompletePayload.
+        // Ideally we should have attachmentSets at one place only.
+        // Send test run complete to logger manager.
+        TestRunCompleteEventArgs testRunCompleteArgs =
+            new(
+                testRunCompletePayload.TestRunCompleteArgs.TestRunStatistics,
+                testRunCompletePayload.TestRunCompleteArgs.IsCanceled,
+                testRunCompletePayload.TestRunCompleteArgs.IsAborted,
+                testRunCompletePayload.TestRunCompleteArgs.Error,
+                testRunCompletePayload.TestRunCompleteArgs.AttachmentSets,
+                testRunCompletePayload.TestRunCompleteArgs.InvokedDataCollectors,
+                _runRequestTimeTracker!.Elapsed);
+        LoggerManager.HandleTestRunComplete(testRunCompleteArgs);
     }
 
     /// <summary>
@@ -580,64 +583,66 @@ private void HandleLoggerManagerTestRunComplete(TestRunCompletePayload testRunCo
     /// <param name="testRunCompletePayload">Test run complete payload.</param>
     /// <param name="message">Updated rawMessage.</param>
     /// <returns></returns>
-    private string UpdateRawMessageWithTelemetryInfo(TestRunCompletePayload testRunCompletePayload, Message message)
+    private string? UpdateRawMessageWithTelemetryInfo(TestRunCompletePayload? testRunCompletePayload, Message? message)
     {
         var rawMessage = default(string);
-        if (_requestData.IsTelemetryOptedIn)
+        if (!_requestData.IsTelemetryOptedIn)
         {
-            if (testRunCompletePayload?.TestRunCompleteArgs != null)
-            {
-                if (testRunCompletePayload.TestRunCompleteArgs.Metrics == null)
-                {
-                    testRunCompletePayload.TestRunCompleteArgs.Metrics = _requestData.MetricsCollection.Metrics;
-                }
-                else
-                {
-                    foreach (var kvp in _requestData.MetricsCollection.Metrics)
-                    {
-                        testRunCompletePayload.TestRunCompleteArgs.Metrics[kvp.Key] = kvp.Value;
-                    }
-                }
-
-                // Fill in the time taken to complete the run
-                var executionTotalTimeTakenForDesignMode = DateTime.UtcNow - _executionStartTime;
-                testRunCompletePayload.TestRunCompleteArgs.Metrics[TelemetryDataConstants.TimeTakenInSecForRun] = executionTotalTimeTakenForDesignMode.TotalSeconds;
-
-                // Add extensions discovered by vstest.console.
-                //
-                // TODO(copoiena):
-                // Doing extension merging here is incorrect because we can end up not merging the
-                // cached extensions for the current process (i.e. vstest.console) and hence have
-                // an incomplete list of discovered extensions. This can happen because this method
-                // is called only if telemetry is opted in (see: HandleRawMessage). We should handle
-                // this merge a level above in order to be consistent, but that means we'd have to
-                // deserialize all raw messages no matter if telemetry is opted in or not and that
-                // would probably mean a performance hit.
-                testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions = TestExtensions.CreateMergedDictionary(
-                    testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions,
-                    TestPluginCache.Instance.TestExtensions?.GetCachedExtensions());
-
-                // Write extensions to telemetry data.
-                TestExtensions.AddExtensionTelemetry(
-                    testRunCompletePayload.TestRunCompleteArgs.Metrics,
-                    testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions);
-            }
+            return rawMessage;
+        }
 
-            if (message is VersionedMessage message1)
+        if (testRunCompletePayload?.TestRunCompleteArgs != null)
+        {
+            if (testRunCompletePayload.TestRunCompleteArgs.Metrics == null)
             {
-                var version = message1.Version;
-
-                rawMessage = _dataSerializer.SerializePayload(
-                    MessageType.ExecutionComplete,
-                    testRunCompletePayload,
-                    version);
+                testRunCompletePayload.TestRunCompleteArgs.Metrics = _requestData.MetricsCollection.Metrics;
             }
             else
             {
-                rawMessage = _dataSerializer.SerializePayload(
-                    MessageType.ExecutionComplete,
-                    testRunCompletePayload);
+                foreach (var kvp in _requestData.MetricsCollection.Metrics)
+                {
+                    testRunCompletePayload.TestRunCompleteArgs.Metrics[kvp.Key] = kvp.Value;
+                }
             }
+
+            // Fill in the time taken to complete the run
+            var executionTotalTimeTakenForDesignMode = DateTime.UtcNow - _executionStartTime;
+            testRunCompletePayload.TestRunCompleteArgs.Metrics[TelemetryDataConstants.TimeTakenInSecForRun] = executionTotalTimeTakenForDesignMode.TotalSeconds;
+
+            // Add extensions discovered by vstest.console.
+            //
+            // TODO(copoiena):
+            // Doing extension merging here is incorrect because we can end up not merging the
+            // cached extensions for the current process (i.e. vstest.console) and hence have
+            // an incomplete list of discovered extensions. This can happen because this method
+            // is called only if telemetry is opted in (see: HandleRawMessage). We should handle
+            // this merge a level above in order to be consistent, but that means we'd have to
+            // deserialize all raw messages no matter if telemetry is opted in or not and that
+            // would probably mean a performance hit.
+            testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions = TestExtensions.CreateMergedDictionary(
+                testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions,
+                TestPluginCache.Instance.TestExtensions?.GetCachedExtensions());
+
+            // Write extensions to telemetry data.
+            TestExtensions.AddExtensionTelemetry(
+                testRunCompletePayload.TestRunCompleteArgs.Metrics,
+                testRunCompletePayload.TestRunCompleteArgs.DiscoveredExtensions);
+        }
+
+        if (message is VersionedMessage message1)
+        {
+            var version = message1.Version;
+
+            rawMessage = _dataSerializer.SerializePayload(
+                MessageType.ExecutionComplete,
+                testRunCompletePayload,
+                version);
+        }
+        else
+        {
+            rawMessage = _dataSerializer.SerializePayload(
+                MessageType.ExecutionComplete,
+                testRunCompletePayload);
         }
 
         return rawMessage;
@@ -690,7 +695,7 @@ protected virtual void Dispose(bool disposing)
                 }
 
                 // Indicate that object has been disposed
-                _runCompletionEvent = null;
+                _runCompletionEvent = null!;
                 _disposed = true;
             }
         }
diff --git a/src/Microsoft.TestPlatform.Client/PublicAPI/PublicAPI.Shipped.txt b/src/Microsoft.TestPlatform.Client/PublicAPI/PublicAPI.Shipped.txt
index db17e826fd..872bef0d70 100644
--- a/src/Microsoft.TestPlatform.Client/PublicAPI/PublicAPI.Shipped.txt
+++ b/src/Microsoft.TestPlatform.Client/PublicAPI/PublicAPI.Shipped.txt
@@ -1,88 +1,89 @@
+#nullable enable
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.ConnectToClientAndProcessRequests(int port, Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager testRequestManager) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.ConnectToClientAndProcessRequests(int port, Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager! testRequestManager) -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.DesignModeClient() -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.Dispose() -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.HandleParentProcessExit() -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.LaunchCustomHost(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo testProcessStartInfo, System.Threading.CancellationToken cancellationToken) -> int
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.onAttachDebuggerAckRecieved -> System.Action<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message>
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.onCustomTestHostLaunchAckReceived -> System.Action<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message>
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.SendRawMessage(string rawMessage) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.SendTestMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string message) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.TestRunMessageHandler(object sender, Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs e) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.LaunchCustomHost(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo! testProcessStartInfo, System.Threading.CancellationToken cancellationToken) -> int
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.onAttachDebuggerAckRecieved -> System.Action<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message!>?
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.onCustomTestHostLaunchAckReceived -> System.Action<Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Message!>?
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.SendRawMessage(string! rawMessage) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.SendTestMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string? message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.TestRunMessageHandler(object? sender, Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs! e) -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.DesignModeTestEventsRegistrar(Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient designModeClient) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.LogWarning(string message) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.RegisterDiscoveryEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.IDiscoveryRequest discoveryRequest) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.RegisterTestRunEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunRequest testRunRequest) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.UnregisterDiscoveryEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.IDiscoveryRequest discoveryRequest) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.UnregisterTestRunEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunRequest testRunRequest) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.DesignModeTestEventsRegistrar(Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient! designModeClient) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.LogWarning(string? message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.RegisterDiscoveryEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.IDiscoveryRequest! discoveryRequest) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.RegisterTestRunEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunRequest! testRunRequest) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.UnregisterDiscoveryEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.IDiscoveryRequest! discoveryRequest) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestEventsRegistrar.UnregisterTestRunEvents(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunRequest! testRunRequest) -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestHostLauncherFactory
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.ConnectToClientAndProcessRequests(int port, Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager testRequestManager) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.ConnectToClientAndProcessRequests(int port, Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager! testRequestManager) -> void
 Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.HandleParentProcessExit() -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.LaunchCustomHost(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo defaultTestHostStartInfo, System.Threading.CancellationToken cancellationToken) -> int
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.SendRawMessage(string rawMessage) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.SendTestMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.LaunchCustomHost(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo! defaultTestHostStartInfo, System.Threading.CancellationToken cancellationToken) -> int
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.SendRawMessage(string! rawMessage) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.SendTestMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string? message) -> void
 Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest
 Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.Abort() -> void
 Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.DiscoverAsync() -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.DiscoveryCriteria.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCriteria
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.DiscoveryCriteria.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCriteria!
 Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.Dispose() -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleDiscoveredTests(System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.TestCase> discoveredTestCases) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleDiscoveryComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCompleteEventArgs discoveryCompleteEventArgs, System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.TestCase> lastChunk) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string message) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleRawMessage(string rawMessage) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveredTests -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveredTestsEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryComplete -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCompleteEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryStart -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryStartEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnRawMessageReceived -> System.EventHandler<string>
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleDiscoveredTests(System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.TestCase!>? discoveredTestCases) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleDiscoveryComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCompleteEventArgs! discoveryCompleteEventArgs, System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.TestCase!>? lastChunk) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string! message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.HandleRawMessage(string! rawMessage) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveredTests -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveredTestsEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryComplete -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryCompleteEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnDiscoveryStart -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryStartEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Discovery.DiscoveryRequest.OnRawMessageReceived -> System.EventHandler<string!>?
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.Abort() -> void
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.CancelAsync() -> void
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.DataCollectionMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.DataCollectionMessageEventArgs>
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.DataCollectionMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.DataCollectionMessageEventArgs!>?
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.Dispose() -> void
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.ExecuteAsync() -> int
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string message) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleRawMessage(string rawMessage) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleTestRunComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCompleteEventArgs runCompleteArgs, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs lastChunkArgs, System.Collections.Generic.ICollection<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet> runContextAttachments, System.Collections.Generic.ICollection<string> executorUris) -> void
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.LaunchProcessWithDebuggerAttached(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo testProcessStartInfo) -> int
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRawMessageReceived -> System.EventHandler<string>
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunCompletion -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCompleteEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunStart -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunStartEventArgs>
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunStatsChange -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs>
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string! message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleRawMessage(string! rawMessage) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleTestRunComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCompleteEventArgs! runCompleteArgs, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs? lastChunkArgs, System.Collections.Generic.ICollection<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet!>? runContextAttachments, System.Collections.Generic.ICollection<string!>? executorUris) -> void
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.LaunchProcessWithDebuggerAttached(Microsoft.VisualStudio.TestPlatform.ObjectModel.TestProcessStartInfo! testProcessStartInfo) -> int
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRawMessageReceived -> System.EventHandler<string!>?
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunCompletion -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCompleteEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunStart -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunStartEventArgs!>?
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.OnRunStatsChange -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs!>?
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.State.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunState
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunConfiguration.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunConfiguration
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunCriteria.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCriteria
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs>
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunConfiguration.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunConfiguration!
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunCriteria.get -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunCriteria!
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.TestRunMessage -> System.EventHandler<Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestRunMessageEventArgs!>?
 Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.WaitForCompletion(int timeout) -> bool
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.AbortTestRun() -> void
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.CancelDiscovery() -> void
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.CancelTestRun() -> void
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.CancelTestRunAttachmentsProcessing() -> void
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.DiscoverTests(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryRequestPayload discoveryPayload, Microsoft.VisualStudio.TestPlatform.Common.Interfaces.ITestDiscoveryEventsRegistrar disoveryEventsRegistrar, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig protocolConfig) -> void
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.InitializeExtensions(System.Collections.Generic.IEnumerable<string> pathToAdditionalExtensions, bool skipExtensionFilters) -> void
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.ProcessTestRunAttachments(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingPayload testRunAttachmentsProcessingPayload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunAttachmentsProcessingEventsHandler testRunAttachmentsProcessingEventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig protocolConfig) -> void
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.DiscoverTests(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.DiscoveryRequestPayload! discoveryPayload, Microsoft.VisualStudio.TestPlatform.Common.Interfaces.ITestDiscoveryEventsRegistrar! disoveryEventsRegistrar, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig! protocolConfig) -> void
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.InitializeExtensions(System.Collections.Generic.IEnumerable<string!>! pathToAdditionalExtensions, bool skipExtensionFilters) -> void
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.ProcessTestRunAttachments(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingPayload! testRunAttachmentsProcessingPayload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestRunAttachmentsProcessingEventsHandler! testRunAttachmentsProcessingEventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig! protocolConfig) -> void
 Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.ResetOptions() -> void
 Microsoft.VisualStudio.TestPlatform.Client.TestPlatformFactory
 Microsoft.VisualStudio.TestPlatform.Client.TestPlatformFactory.TestPlatformFactory() -> void
 Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string message) -> void
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleProcessedAttachmentsChunk(System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet> attachments) -> void
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleRawMessage(string rawMessage) -> void
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleTestRunAttachmentsProcessingComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingCompleteEventArgs attachmentsProcessingCompleteEventArgs, System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet> lastChunk) -> void
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleTestRunAttachmentsProcessingProgress(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingProgressEventArgs attachmentsProcessingProgressEventArgs) -> void
-Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.TestRunAttachmentsProcessingEventsHandler(Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationManager communicationManager) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleLogMessage(Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging.TestMessageLevel level, string! message) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleProcessedAttachmentsChunk(System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet!>! attachments) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleRawMessage(string! rawMessage) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleTestRunAttachmentsProcessingComplete(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingCompleteEventArgs! attachmentsProcessingCompleteEventArgs, System.Collections.Generic.IEnumerable<Microsoft.VisualStudio.TestPlatform.ObjectModel.AttachmentSet!>! lastChunk) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.HandleTestRunAttachmentsProcessingProgress(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunAttachmentsProcessingProgressEventArgs! attachmentsProcessingProgressEventArgs) -> void
+Microsoft.VisualStudio.TestPlatform.Client.TestRunAttachmentsProcessing.TestRunAttachmentsProcessingEventsHandler.TestRunAttachmentsProcessingEventsHandler(Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces.ICommunicationManager! communicationManager) -> void
 static Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.Initialize() -> void
-static Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.Instance.get -> Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient
-static Microsoft.VisualStudio.TestPlatform.Client.TestPlatformFactory.GetTestPlatform() -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestPlatform
+static Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.Instance.get -> Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient?
+static Microsoft.VisualStudio.TestPlatform.Client.TestPlatformFactory.GetTestPlatform() -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestPlatform!
 virtual Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.Dispose(bool disposing) -> void
-virtual Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleTestRunStatsChange(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs testRunChangedArgs) -> void
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.StopTestSession(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads.StopTestSessionPayload payload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestSessionEventsHandler eventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig protocolConfig) -> void
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo attachDebuggerInfo, System.Threading.CancellationToken cancellationToken) -> bool
-Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo attachDebuggerInfo, System.Threading.CancellationToken cancellationToken) -> bool
-Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo attachDebuggerInfo) -> bool
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.RunTests(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunRequestPayload testRunRequestPayLoad, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3 customTestHostLauncher, Microsoft.VisualStudio.TestPlatform.Common.Interfaces.ITestRunEventsRegistrar testRunEventsRegistrar, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig protocolConfig) -> void
-Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.StartTestSession(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads.StartTestSessionPayload payload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3 testHostLauncher, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestSessionEventsHandler eventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig protocolConfig) -> void
-static Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestHostLauncherFactory.GetCustomHostLauncherForTestRun(Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient designModeClient, bool debuggingEnabled) -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3
+virtual Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.HandleTestRunStatsChange(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunChangedEventArgs? testRunChangedArgs) -> void
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.StopTestSession(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads.StopTestSessionPayload! payload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestSessionEventsHandler! eventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig! protocolConfig) -> void
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeClient.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo! attachDebuggerInfo, System.Threading.CancellationToken cancellationToken) -> bool
+Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo! attachDebuggerInfo, System.Threading.CancellationToken cancellationToken) -> bool
+Microsoft.VisualStudio.TestPlatform.Client.Execution.TestRunRequest.AttachDebuggerToProcess(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.AttachDebuggerInfo! attachDebuggerInfo) -> bool
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.RunTests(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.TestRunRequestPayload! testRunRequestPayLoad, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3? customTestHostLauncher, Microsoft.VisualStudio.TestPlatform.Common.Interfaces.ITestRunEventsRegistrar! testRunEventsRegistrar, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig! protocolConfig) -> void
+Microsoft.VisualStudio.TestPlatform.Client.RequestHelper.ITestRequestManager.StartTestSession(Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads.StartTestSessionPayload! payload, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3? testHostLauncher, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ITestSessionEventsHandler! eventsHandler, Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.ProtocolConfig! protocolConfig) -> void
+static Microsoft.VisualStudio.TestPlatform.Client.DesignMode.DesignModeTestHostLauncherFactory.GetCustomHostLauncherForTestRun(Microsoft.VisualStudio.TestPlatform.Client.DesignMode.IDesignModeClient! designModeClient, bool debuggingEnabled) -> Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces.ITestHostLauncher3!
diff --git a/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs b/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
index 5108a1591d..d44026f148 100644
--- a/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
+++ b/src/Microsoft.TestPlatform.Client/RequestHelper/ITestRequestManager.cs
@@ -10,8 +10,6 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Interfaces;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client.RequestHelper;
 
 /// <summary>
@@ -56,7 +54,7 @@ void DiscoverTests(
     /// <param name="protocolConfig">Protocol related information.</param>
     void RunTests(
         TestRunRequestPayload testRunRequestPayLoad,
-        ITestHostLauncher3 customTestHostLauncher,
+        ITestHostLauncher3? customTestHostLauncher,
         ITestRunEventsRegistrar testRunEventsRegistrar,
         ProtocolConfig protocolConfig);
 
@@ -86,14 +84,14 @@ void ProcessTestRunAttachments(
     /// <param name="protocolConfig">Protocol related information.</param>
     void StartTestSession(
         StartTestSessionPayload payload,
-        ITestHostLauncher3 testHostLauncher,
+        ITestHostLauncher3? testHostLauncher,
         ITestSessionEventsHandler eventsHandler,
         ProtocolConfig protocolConfig);
 
     /// <summary>
     /// Stops a test session.
     /// </summary>
-    /// 
+    ///
     /// <param name="testSessionInfo">The stop test session payload.</param>
     /// <param name="eventsHandler">The events handler.</param>
     /// <param name="protocolConfig">Protocol related information.</param>
diff --git a/src/Microsoft.TestPlatform.Client/TestPlatform.cs b/src/Microsoft.TestPlatform.Client/TestPlatform.cs
index 79de15d7ee..a07f6618db 100644
--- a/src/Microsoft.TestPlatform.Client/TestPlatform.cs
+++ b/src/Microsoft.TestPlatform.Client/TestPlatform.cs
@@ -26,8 +26,6 @@
 
 using ClientResources = Microsoft.VisualStudio.TestPlatform.Client.Resources.Resources;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client;
 
 /// <summary>
@@ -81,7 +79,7 @@ protected internal TestPlatform(
     public IDiscoveryRequest CreateDiscoveryRequest(
         IRequestData requestData,
         DiscoveryCriteria discoveryCriteria,
-        TestPlatformOptions options,
+        TestPlatformOptions? options,
         Dictionary<string, SourceDetail> sourceToSourceDetailMap)
     {
         ValidateArg.NotNull(discoveryCriteria, nameof(discoveryCriteria));
@@ -102,7 +100,7 @@ public IDiscoveryRequest CreateDiscoveryRequest(
     public ITestRunRequest CreateTestRunRequest(
         IRequestData requestData,
         TestRunCriteria testRunCriteria,
-        TestPlatformOptions options,
+        TestPlatformOptions? options,
         Dictionary<string, SourceDetail> sourceToSourceDetailMap)
     {
         ValidateArg.NotNull(testRunCriteria, nameof(testRunCriteria));
@@ -139,7 +137,7 @@ public bool StartTestSession(
             return false;
         }
 
-        IProxyTestSessionManager testSessionManager = _testEngine.GetTestSessionManager(requestData, testSessionCriteria, sourceToSourceDetailMap);
+        IProxyTestSessionManager? testSessionManager = _testEngine.GetTestSessionManager(requestData, testSessionCriteria, sourceToSourceDetailMap);
         if (testSessionManager == null)
         {
             // The test session manager is null because the combination of runsettings and
@@ -191,7 +189,7 @@ public void ClearExtensions()
     }
 
     private static void ThrowExceptionIfTestHostManagerIsNull(
-        ITestRuntimeProvider testHostManager,
+        ITestRuntimeProvider? testHostManager,
         string settingsXml)
     {
         if (testHostManager == null)
diff --git a/src/Microsoft.TestPlatform.Client/TestPlatformFactory.cs b/src/Microsoft.TestPlatform.Client/TestPlatformFactory.cs
index c1de82f380..2e703efd4a 100644
--- a/src/Microsoft.TestPlatform.Client/TestPlatformFactory.cs
+++ b/src/Microsoft.TestPlatform.Client/TestPlatformFactory.cs
@@ -3,8 +3,6 @@
 
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client;
 
 /// <summary>
@@ -12,7 +10,7 @@ namespace Microsoft.VisualStudio.TestPlatform.Client;
 /// </summary>
 public class TestPlatformFactory
 {
-    private static ITestPlatform s_testPlatform;
+    private static ITestPlatform? s_testPlatform;
 
     /// <summary>
     /// Gets an instance of the test platform.
diff --git a/src/Microsoft.TestPlatform.Client/TestSession/TestSessionEventsHandler.cs b/src/Microsoft.TestPlatform.Client/TestSession/TestSessionEventsHandler.cs
index e7f195a884..cb1860e581 100644
--- a/src/Microsoft.TestPlatform.Client/TestSession/TestSessionEventsHandler.cs
+++ b/src/Microsoft.TestPlatform.Client/TestSession/TestSessionEventsHandler.cs
@@ -2,15 +2,11 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Interfaces;
-
 using Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.ObjectModel;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Client.Payloads;
-
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
 
-#nullable disable
-
 namespace Microsoft.VisualStudio.TestPlatform.Client;
 
 /// <summary>
diff --git a/test/Microsoft.TestPlatform.Client.UnitTests/TestPlatformTests.cs b/test/Microsoft.TestPlatform.Client.UnitTests/TestPlatformTests.cs
index 69d039d7e1..ae968206a4 100644
--- a/test/Microsoft.TestPlatform.Client.UnitTests/TestPlatformTests.cs
+++ b/test/Microsoft.TestPlatform.Client.UnitTests/TestPlatformTests.cs
@@ -105,7 +105,7 @@ public void CreateDiscoveryRequestThrowsIfDiscoveryCriteriaIsNull()
     {
         TestPlatform tp = new();
 
-        Assert.ThrowsException<ArgumentNullException>(() => tp.CreateDiscoveryRequest(_mockRequestData.Object, null, new TestPlatformOptions(), It.IsAny<Dictionary<string, SourceDetail>>()));
+        Assert.ThrowsException<ArgumentNullException>(() => tp.CreateDiscoveryRequest(_mockRequestData.Object, null!, new TestPlatformOptions(), It.IsAny<Dictionary<string, SourceDetail>>()));
     }
 
     [TestMethod]
@@ -283,7 +283,7 @@ public void CreateTestRunRequestThrowsIfTestRunCriteriaIsNull()
     {
         var tp = new TestPlatform();
 
-        Assert.ThrowsException<ArgumentNullException>(() => tp.CreateTestRunRequest(_mockRequestData.Object, null, new TestPlatformOptions(), It.IsAny<Dictionary<string, SourceDetail>>()));
+        Assert.ThrowsException<ArgumentNullException>(() => tp.CreateTestRunRequest(_mockRequestData.Object, null!, new TestPlatformOptions(), It.IsAny<Dictionary<string, SourceDetail>>()));
     }
 
     /// <summary>
@@ -427,7 +427,7 @@ public void StartTestSessionShouldThrowExceptionIfTestSessionCriteriaIsNull()
         Assert.ThrowsException<ArgumentNullException>(() =>
             tp.StartTestSession(
                 new Mock<IRequestData>().Object,
-                null,
+                null!,
                 new Mock<ITestSessionEventsHandler>().Object,
                 new Dictionary<string, SourceDetail>()));
     }