Fix MSTest live output deadlock

src/Adapter/MSTestAdapter.PlatformServices/Execution/UnitTestRunner.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 #if NETFRAMEWORK
@@ -112,15 +112,62 @@ private static void ConfigureOutputRouting(TestOutputCaptureMode mode)
             Func<TestOutputCaptureMode> modeProvider = static () => MSTestSettings.CurrentSettings.OutputCaptureMode;
             TextWriter originalOut = Console.Out;
             TextWriter originalError = Console.Error;
-            TestContextImplementation.ConfigureLiveOutputWriter(originalOut);
+            TextWriter liveOutputWriter = CreateLiveOutputWriter(Console.OpenStandardOutput(), Console.OutputEncoding);
+            TestContextImplementation.ConfigureLiveOutputWriter(liveOutputWriter);
             Console.SetOut(new ConsoleOutRouter(originalOut, modeProvider));
             Console.SetError(new ConsoleErrorRouter(originalError, modeProvider));
-            Trace.Listeners.Add(new TextWriterTraceListener(new TraceTextWriter(originalOut, modeProvider)));
+            Trace.Listeners.Add(new TextWriterTraceListener(new TraceTextWriter(liveOutputWriter, modeProvider)));
 
             s_outputRoutingInstalled = true;
         }
     }
 
+    internal static TextWriter CreateLiveOutputWriter(Stream standardOutput, Encoding encoding)
+    {
+        Encoding preamblelessEncoding = encoding.GetPreamble().Length == 0
+            ? encoding
+            : new PreamblelessEncoding(encoding);
+        var streamWriter = new StreamWriter(standardOutput, preamblelessEncoding, bufferSize: 1024, leaveOpen: true)
+        {
+            AutoFlush = true,
+        };
+
+        return TextWriter.Synchronized(streamWriter);
+    }
+
+    private sealed class PreamblelessEncoding(Encoding encoding) : Encoding
+    {
+        public override int CodePage => encoding.CodePage;
+
+        public override string EncodingName => encoding.EncodingName;
+
+        public override bool IsSingleByte => encoding.IsSingleByte;
+
+        public override string WebName => encoding.WebName;
+
+        public override Decoder GetDecoder() => encoding.GetDecoder();
+
+        public override Encoder GetEncoder() => encoding.GetEncoder();
+
+        public override int GetByteCount(char[] chars, int index, int count)
+            => encoding.GetByteCount(chars, index, count);
+
+        public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex)
+            => encoding.GetBytes(chars, charIndex, charCount, bytes, byteIndex);
+
+        public override int GetCharCount(byte[] bytes, int index, int count)
+            => encoding.GetCharCount(bytes, index, count);
+
+        public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex)
+            => encoding.GetChars(bytes, byteIndex, byteCount, chars, charIndex);
+
+        public override int GetMaxByteCount(int charCount) => encoding.GetMaxByteCount(charCount);
+
+        public override int GetMaxCharCount(int byteCount) => encoding.GetMaxCharCount(byteCount);
+
+        public override byte[] GetPreamble() => [];
+    }
+
 #pragma warning disable CA1822 // Mark members as static
     public void Cancel()
         => PlatformServiceProvider.Instance.TestRunCancellationToken?.Cancel();

src/Adapter/MSTestAdapter.PlatformServices/InternalAPI/InternalAPI.Unshipped.txt

@@ -35,6 +35,8 @@ Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.TestContextIm
 static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution.TestMethodInfo.ParameterMetadataScanCount.get -> int
 static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution.TestMethodInfo.ResetParameterMetadataCacheForTesting() -> void
 static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution.TestMethodInfo.SetParameterMetadataScanCallbackForTesting(System.Action? callback) -> void
+static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution.UnitTestRunner.CreateLiveOutputWriter(System.IO.Stream! standardOutput, System.Text.Encoding! encoding) -> System.IO.TextWriter!
 static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Helpers.RuntimeContext.IsMultiThreaded.get -> bool
 static Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.MSTestDiscovererHelpers.GetSettingsExceptionMessage(Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.ObjectModel.AdapterSettingsException! ex) -> string!
 static Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.TestContextImplementation.ConfigureLiveOutputWriter(System.IO.TextWriter! liveOutputWriter) -> void
+static Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.TestContextImplementation.SetLiveOutputWriterForTesting(System.IO.TextWriter! liveOutputWriter) -> System.IDisposable!

src/Adapter/MSTestAdapter.PlatformServices/Services/TestContextImplementation.LiveOutputScope.cs

@@ -23,10 +23,24 @@ internal void Deactivate()
             => Volatile.Write(ref _isActive, 0);
     }
 
+    private sealed class LiveOutputWriterScope(TextWriter? previousLiveOutputWriter) : IDisposable
+    {
+        public void Dispose()
+            => Volatile.Write(ref s_liveOutputWriter, previousLiveOutputWriter);
+    }
+
     // This writer is captured together with the process-wide Console routers and shares their install-once lifetime.
     internal static void ConfigureLiveOutputWriter(TextWriter liveOutputWriter)
         => Volatile.Write(ref s_liveOutputWriter, liveOutputWriter);
 
+    internal static IDisposable SetLiveOutputWriterForTesting(TextWriter liveOutputWriter)
+    {
+        TextWriter? previousLiveOutputWriter = Volatile.Read(ref s_liveOutputWriter);
+        Volatile.Write(ref s_liveOutputWriter, liveOutputWriter);
+
+        return new LiveOutputWriterScope(previousLiveOutputWriter);
+    }
+
     private void WriteLive(string? message, bool appendLine)
     {
         if (_liveOutputWriter is null