Change StdioServerTransportTests to use Debug instead of Trace logging level

Address feedback from PR #1191: The class-level LoggerFactory override was removed
from the constructor (now uses base class default of Debug). The trace-level
logging tests now create their own local MockLoggerProvider and trace-level
LoggerFactory to properly test Trace-level logging without affecting other tests.

Co-authored-by: stephentoub <[email protected]>

Author: Copilot

tests/ModelContextProtocol.Tests/Transport/StdioServerTransportTests.cs

@@ -22,14 +22,6 @@ public StdioServerTransportTests(ITestOutputHelper testOutputHelper)
             InitializationTimeout = TimeSpan.FromSeconds(10),
             ServerInstructions = "Test Instructions"
         };
-
-        // Override the LoggerFactory to use Trace level for testing Trace-level logging
-        LoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
-        {
-            builder.AddProvider(XunitLoggerProvider);
-            builder.AddProvider(MockLoggerProvider);
-            builder.SetMinimumLevel(LogLevel.Trace);
-        });
     }
 
     [Fact(Skip="https://github.com/modelcontextprotocol/csharp-sdk/issues/143")]
@@ -207,19 +199,27 @@ public async Task SendMessageAsync_Should_Preserve_Unicode_Characters()
     public async Task SendMessageAsync_Should_Log_At_Trace_Level()
     {
         // Arrange
+        var mockLoggerProvider = new MockLoggerProvider();
+        using var traceLoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        {
+            builder.AddProvider(XunitLoggerProvider);
+            builder.AddProvider(mockLoggerProvider);
+            builder.SetMinimumLevel(LogLevel.Trace);
+        });
+
         using var output = new MemoryStream();
 
         await using var transport = new StreamServerTransport(
             new Pipe().Reader.AsStream(),
             output,
-            loggerFactory: LoggerFactory);
+            loggerFactory: traceLoggerFactory);
 
         // Act
         var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
         await transport.SendMessageAsync(message, TestContext.Current.CancellationToken);
 
         // Assert
-        var traceLogMessages = MockLoggerProvider.LogMessages
+        var traceLogMessages = mockLoggerProvider.LogMessages
             .Where(x => x.LogLevel == LogLevel.Trace && x.Message.Contains("transport sending message"))
             .ToList();
 
@@ -231,6 +231,14 @@ public async Task SendMessageAsync_Should_Log_At_Trace_Level()
     public async Task ReadMessagesAsync_Should_Log_Received_At_Trace_Level()
     {
         // Arrange
+        var mockLoggerProvider = new MockLoggerProvider();
+        using var traceLoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        {
+            builder.AddProvider(XunitLoggerProvider);
+            builder.AddProvider(mockLoggerProvider);
+            builder.SetMinimumLevel(LogLevel.Trace);
+        });
+
         var message = new JsonRpcRequest { Method = "test", Id = new RequestId(99) };
         var json = JsonSerializer.Serialize(message, McpJsonUtilities.DefaultOptions);
 
@@ -240,7 +248,7 @@ public async Task ReadMessagesAsync_Should_Log_Received_At_Trace_Level()
         await using var transport = new StreamServerTransport(
             input,
             Stream.Null,
-            loggerFactory: LoggerFactory);
+            loggerFactory: traceLoggerFactory);
 
         // Act
         await pipe.Writer.WriteAsync(Encoding.UTF8.GetBytes($"{json}\n"), TestContext.Current.CancellationToken);
@@ -250,7 +258,7 @@ public async Task ReadMessagesAsync_Should_Log_Received_At_Trace_Level()
         Assert.True(canRead, "Nothing to read here from transport message reader");
 
         // Assert
-        var traceLogMessages = MockLoggerProvider.LogMessages
+        var traceLogMessages = mockLoggerProvider.LogMessages
             .Where(x => x.LogLevel == LogLevel.Trace && x.Message.Contains("transport received message"))
             .ToList();