Add XunitLoggerProvider (#81)

* Add XunitLoggerProvider

* Avoid logging to stale ITestOutputHelper in fixture disposal

* Use LoggedTest base class everywhere an ILoggerFactory is used

tests/ModelContextProtocol.TestSseServer/Program.cs

@@ -10,9 +10,10 @@ namespace ModelContextProtocol.TestSseServer;
 
 public class Program
 {
-    private static ILoggerFactory CreateLoggerFactory()
+    private static ILoggerFactory CreateLoggerFactory() => LoggerFactory.Create(ConfigureSerilog);
+
+    public static void ConfigureSerilog(ILoggingBuilder loggingBuilder)
     {
-        // Use serilog
         Log.Logger = new LoggerConfiguration()
             .MinimumLevel.Verbose() // Capture all log levels
             .WriteTo.File(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "logs", "TestServer_.log"),
@@ -21,15 +22,12 @@ public class Program
             .CreateLogger();
 
         var logsPath = Path.Combine(AppContext.BaseDirectory, "testserver.log");
-        return LoggerFactory.Create(builder =>
+        loggingBuilder.AddSerilog();
-        {
-            builder.AddSerilog();
-        });
     }
 
     public static Task Main(string[] args) => MainAsync(args);
 
-    public static async Task MainAsync(string[] args, CancellationToken cancellationToken = default)
+    public static async Task MainAsync(string[] args, ILoggerFactory? loggerFactory = null, CancellationToken cancellationToken = default)
     {
         Console.WriteLine("Starting server...");
 
@@ -385,7 +383,7 @@ public class Program
             },
         };
 
-        using var loggerFactory = CreateLoggerFactory();
+        loggerFactory ??= CreateLoggerFactory();
         server = McpServerFactory.Create(new HttpListenerSseServerTransport("TestServer", 3001, loggerFactory), options, loggerFactory);
 
         Console.WriteLine("Server initialized.");

tests/ModelContextProtocol.Tests/ClientIntegrationTestFixture.cs

@@ -5,9 +5,10 @@ using Microsoft.Extensions.Logging;
 
 namespace ModelContextProtocol.Tests;
 
-public class ClientIntegrationTestFixture : IDisposable
+public class ClientIntegrationTestFixture
 {
-    public ILoggerFactory LoggerFactory { get; }
+    private ILoggerFactory? _loggerFactory;
+
     public McpClientOptions DefaultOptions { get; }
     public McpServerConfig EverythingServerConfig { get; }
     public McpServerConfig TestServerConfig { get; }
@@ -16,10 +17,6 @@ public class ClientIntegrationTestFixture : IDisposable
 
     public ClientIntegrationTestFixture()
     {
-        LoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
-            builder.AddConsole()
-            .SetMinimumLevel(LogLevel.Debug));
-
         DefaultOptions = new()
         {
             ClientInfo = new() { Name = "IntegrationTestClient", Version = "1.0.0" },
@@ -56,17 +53,16 @@ public class ClientIntegrationTestFixture : IDisposable
         }
     }
 
+    public void Initialize(ILoggerFactory loggerFactory)
+    {
+        _loggerFactory = loggerFactory;
+    }
+
     public Task<IMcpClient> CreateClientAsync(string clientId, McpClientOptions? clientOptions = null) =>
         McpClientFactory.CreateAsync(clientId switch
         {
             "everything" => EverythingServerConfig,
             "test_server" => TestServerConfig,
             _ => throw new ArgumentException($"Unknown client ID: {clientId}")
-        }, clientOptions ?? DefaultOptions, loggerFactory: LoggerFactory);
+        }, clientOptions ?? DefaultOptions, loggerFactory: _loggerFactory);
-
-    public void Dispose()
-    {
-        LoggerFactory?.Dispose();
-        GC.SuppressFinalize(this);
-    }
 }

tests/ModelContextProtocol.Tests/ClientIntegrationTests.cs

@@ -6,6 +6,7 @@ using ModelContextProtocol.Protocol.Messages;
 using System.Text.Json;
 using ModelContextProtocol.Configuration;
 using ModelContextProtocol.Protocol.Transport;
+using ModelContextProtocol.Tests.Utils;
 using Xunit.Sdk;
 using System.Text.Encodings.Web;
 using System.Text.Json.Serialization.Metadata;
@@ -13,15 +14,17 @@ using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Tests;
 
-public class ClientIntegrationTests : IClassFixture<ClientIntegrationTestFixture>
+public class ClientIntegrationTests : LoggedTest, IClassFixture<ClientIntegrationTestFixture>
 {
     private static readonly string? s_openAIKey = Environment.GetEnvironmentVariable("AI:OpenAI:ApiKey")!;
 
     private readonly ClientIntegrationTestFixture _fixture;
 
-    public ClientIntegrationTests(ClientIntegrationTestFixture fixture)
+    public ClientIntegrationTests(ClientIntegrationTestFixture fixture, ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _fixture = fixture;
+        _fixture.Initialize(LoggerFactory);
     }
 
     public static IEnumerable<object[]> GetClients() =>
@@ -474,7 +477,7 @@ public class ClientIntegrationTests : IClassFixture<ClientIntegrationTestFixture
         await using var client = await McpClientFactory.CreateAsync(
             serverConfig, 
             clientOptions, 
-            loggerFactory: _fixture.LoggerFactory, 
+            loggerFactory: LoggerFactory, 
             cancellationToken: TestContext.Current.CancellationToken);
 
         // act

tests/ModelContextProtocol.Tests/Server/McpServerFactoryTests.cs

@@ -1,18 +1,18 @@
 using ModelContextProtocol.Protocol.Transport;
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Server;
-using Microsoft.Extensions.Logging.Abstractions;
+using ModelContextProtocol.Tests.Utils;
 using Moq;
 
 namespace ModelContextProtocol.Tests.Server;
 
-public class McpServerFactoryTests
+public class McpServerFactoryTests : LoggedTest
 {
     private readonly Mock<IServerTransport> _serverTransport;
     private readonly McpServerOptions _options;
-    private readonly IServiceProvider _serviceProvider;
 
-    public McpServerFactoryTests()
+    public McpServerFactoryTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _serverTransport = new Mock<IServerTransport>();
         _options = new McpServerOptions
@@ -21,14 +21,13 @@ public class McpServerFactoryTests
             ProtocolVersion = "1.0",
             InitializationTimeout = TimeSpan.FromSeconds(30)
         };
-        _serviceProvider = new Mock<IServiceProvider>().Object;
     }
 
     [Fact]
     public async Task Create_Should_Initialize_With_Valid_Parameters()
     {
         // Arrange & Act
-        await using IMcpServer server = McpServerFactory.Create(_serverTransport.Object, _options, NullLoggerFactory.Instance);
+        await using IMcpServer server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory);
 
         // Assert
         Assert.NotNull(server);
@@ -38,13 +37,13 @@ public class McpServerFactoryTests
     public void Constructor_Throws_For_Null_ServerTransport()
     {
         // Arrange, Act & Assert
-        Assert.Throws<ArgumentNullException>("serverTransport", () => McpServerFactory.Create(null!, _options, NullLoggerFactory.Instance));
+        Assert.Throws<ArgumentNullException>("serverTransport", () => McpServerFactory.Create(null!, _options, LoggerFactory));
     }
 
     [Fact]
     public void Constructor_Throws_For_Null_Options()
     {
         // Arrange, Act & Assert
-        Assert.Throws<ArgumentNullException>("serverOptions", () => McpServerFactory.Create(_serverTransport.Object, null!, NullLoggerFactory.Instance));
+        Assert.Throws<ArgumentNullException>("serverOptions", () => McpServerFactory.Create(_serverTransport.Object, null!, LoggerFactory));
     }
 }

tests/ModelContextProtocol.Tests/Server/McpServerTests.cs

@@ -11,20 +11,18 @@ using System.Reflection;
 
 namespace ModelContextProtocol.Tests.Server;
 
-public class McpServerTests
+public class McpServerTests : LoggedTest
 {
     private readonly Mock<IServerTransport> _serverTransport;
-    private readonly Mock<ILoggerFactory> _loggerFactory;
     private readonly Mock<ILogger> _logger;
     private readonly McpServerOptions _options;
     private readonly IServiceProvider _serviceProvider;
 
-    public McpServerTests()
+    public McpServerTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _serverTransport = new Mock<IServerTransport>();
-        _loggerFactory = new Mock<ILoggerFactory>();
         _logger = new Mock<ILogger>();
-        _loggerFactory.Setup(f => f.CreateLogger(It.IsAny<string>())).Returns(_logger.Object);
         _options = CreateOptions();
         _serviceProvider = new Mock<IServiceProvider>().Object;
     }
@@ -44,7 +42,7 @@ public class McpServerTests
     public async Task Constructor_Should_Initialize_With_Valid_Parameters()
     {
         // Arrange & Act
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
 
         // Assert
         Assert.NotNull(server);
@@ -54,14 +52,14 @@ public class McpServerTests
     public void Constructor_Throws_For_Null_Transport()
     {
         // Arrange, Act & Assert
-        Assert.Throws<ArgumentNullException>(() => McpServerFactory.Create(null!, _options, _loggerFactory.Object, _serviceProvider));
+        Assert.Throws<ArgumentNullException>(() => McpServerFactory.Create(null!, _options, LoggerFactory, _serviceProvider));
     }
 
     [Fact]
     public void Constructor_Throws_For_Null_Options()
     {
         // Arrange, Act & Assert
-        Assert.Throws<ArgumentNullException>(() => McpServerFactory.Create(_serverTransport.Object, null!, _loggerFactory.Object, _serviceProvider));
+        Assert.Throws<ArgumentNullException>(() => McpServerFactory.Create(_serverTransport.Object, null!, LoggerFactory, _serviceProvider));
     }
 
     [Fact]
@@ -78,7 +76,7 @@ public class McpServerTests
     public async Task Constructor_Does_Not_Throw_For_Null_ServiceProvider()
     {
         // Arrange & Act
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, null);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, null);
 
         // Assert
         Assert.NotNull(server);
@@ -88,7 +86,7 @@ public class McpServerTests
     public async Task StartAsync_Should_Throw_InvalidOperationException_If_Already_Initializing()
     {
         // Arrange
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
         var task = server.StartAsync(TestContext.Current.CancellationToken);
 
         // Act & Assert
@@ -101,7 +99,7 @@ public class McpServerTests
     public async Task StartAsync_Should_Do_Nothing_If_Already_Initialized()
     {
         // Arrange
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
         SetInitialized(server, true);
 
         await server.StartAsync(TestContext.Current.CancellationToken);
@@ -114,7 +112,7 @@ public class McpServerTests
     public async Task StartAsync_ShouldStartListening()
     {
         // Arrange
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
 
         // Act
         await server.StartAsync(TestContext.Current.CancellationToken);
@@ -127,7 +125,7 @@ public class McpServerTests
     public async Task StartAsync_Sets_Initialized_After_Transport_Responses_Initialized_Notification()
     {
         await using var transport = new TestServerTransport();
-        await using var server = McpServerFactory.Create(transport, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(transport, _options, LoggerFactory, _serviceProvider);
 
         await server.StartAsync(TestContext.Current.CancellationToken);
 
@@ -147,7 +145,7 @@ public class McpServerTests
     public async Task RequestSamplingAsync_Should_Throw_McpServerException_If_Client_Does_Not_Support_Sampling()
     {
         // Arrange
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
         SetClientCapabilities(server, new ClientCapabilities());
 
         var action = () => server.RequestSamplingAsync(new CreateMessageRequestParams { Messages = [] }, CancellationToken.None);
@@ -161,7 +159,7 @@ public class McpServerTests
     {
         // Arrange
         await using var transport = new TestServerTransport();
-        await using var server = McpServerFactory.Create(transport, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(transport, _options, LoggerFactory, _serviceProvider);
         SetClientCapabilities(server, new ClientCapabilities { Sampling = new SamplingCapability() });
 
         await server.StartAsync(TestContext.Current.CancellationToken);
@@ -179,7 +177,7 @@ public class McpServerTests
     public async Task RequestRootsAsync_Should_Throw_McpServerException_If_Client_Does_Not_Support_Roots()
     {
         // Arrange
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
         SetClientCapabilities(server, new ClientCapabilities());
 
         // Act & Assert
@@ -191,7 +189,7 @@ public class McpServerTests
     {
         // Arrange
         await using var transport = new TestServerTransport();
-        await using var server = McpServerFactory.Create(transport, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(transport, _options, LoggerFactory, _serviceProvider);
         SetClientCapabilities(server, new ClientCapabilities { Roots = new RootsCapability() });
         await server.StartAsync(TestContext.Current.CancellationToken);
 
@@ -208,7 +206,7 @@ public class McpServerTests
     [Fact]
     public async Task Throws_Exception_If_Not_Connected()
     {
-        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(_serverTransport.Object, _options, LoggerFactory, _serviceProvider);
         SetClientCapabilities(server, new ClientCapabilities { Roots = new RootsCapability() });
         _serverTransport.SetupGet(t => t.IsConnected).Returns(false);
 
@@ -555,7 +553,7 @@ public class McpServerTests
         var options = CreateOptions(serverCapabilities);
         configureOptions?.Invoke(options);
 
-        await using var server = McpServerFactory.Create(transport, options, _loggerFactory.Object, _serviceProvider);
+        await using var server = McpServerFactory.Create(transport, options, LoggerFactory, _serviceProvider);
 
         await server.StartAsync();
 
@@ -587,7 +585,7 @@ public class McpServerTests
         await using var transport = new TestServerTransport();
         var options = CreateOptions(serverCapabilities);
 
-        Assert.Throws<McpServerException>(() => McpServerFactory.Create(transport, options, _loggerFactory.Object, _serviceProvider));
+        Assert.Throws<McpServerException>(() => McpServerFactory.Create(transport, options, LoggerFactory, _serviceProvider));
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/SseServerIntegrationTestFixture.cs

@@ -2,23 +2,29 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Configuration;
 using ModelContextProtocol.Protocol.Transport;
+using ModelContextProtocol.Test.Utils;
+using ModelContextProtocol.TestSseServer;
 
 namespace ModelContextProtocol.Tests;
 
 public class SseServerIntegrationTestFixture : IAsyncDisposable
 {
-    private readonly CancellationTokenSource _stopCts = new();
     private readonly Task _serverTask;
+    private readonly CancellationTokenSource _stopCts = new();
+
+    private readonly DelegatingTestOutputHelper _delegatingTestOutputHelper = new();
+    private readonly ILoggerFactory _redirectingLoggerFactory;
 
-    public ILoggerFactory LoggerFactory { get; }
     public McpClientOptions DefaultOptions { get; }
     public McpServerConfig DefaultConfig { get; }
 
     public SseServerIntegrationTestFixture()
     {
-        LoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        _redirectingLoggerFactory = LoggerFactory.Create(builder =>
-            builder.AddConsole()
+        {
-            .SetMinimumLevel(LogLevel.Debug));
+            Program.ConfigureSerilog(builder);
+            builder.AddProvider(new XunitLoggerProvider(_delegatingTestOutputHelper));
+        });
 
         DefaultOptions = new()
         {
@@ -34,12 +40,17 @@ public class SseServerIntegrationTestFixture : IAsyncDisposable
             Location = "http://localhost:3001/sse"
         };
 
-        _serverTask = TestSseServer.Program.MainAsync([], _stopCts.Token);
+        _serverTask = Program.MainAsync([], _redirectingLoggerFactory, _stopCts.Token);
+    }
+
+    public void Initialize(ITestOutputHelper output)
+    {
+        _delegatingTestOutputHelper.CurrentTestOutputHelper = output;
     }
 
     public async ValueTask DisposeAsync()
     {
-        LoggerFactory.Dispose();
+        _delegatingTestOutputHelper.CurrentTestOutputHelper = null;
         _stopCts.Cancel();
         try
         {
@@ -48,6 +59,19 @@ public class SseServerIntegrationTestFixture : IAsyncDisposable
         catch (OperationCanceledException)
         {
         }
+        _redirectingLoggerFactory.Dispose();
         _stopCts.Dispose();
     }
+
+    private class DelegatingTestOutputHelper() : ITestOutputHelper
+    {
+        public ITestOutputHelper? CurrentTestOutputHelper { get; set; }
+
+        public string Output => CurrentTestOutputHelper?.Output ?? string.Empty;
+
+        public void Write(string message) => CurrentTestOutputHelper?.Write(message);
+        public void Write(string format, params object[] args) => CurrentTestOutputHelper?.Write(format, args);
+        public void WriteLine(string message) => CurrentTestOutputHelper?.WriteLine(message);
+        public void WriteLine(string format, params object[] args) => CurrentTestOutputHelper?.WriteLine(format, args);
+    }
 }

tests/ModelContextProtocol.Tests/SseServerIntegrationTests.cs

@@ -1,15 +1,18 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol.Types;
+using ModelContextProtocol.Tests.Utils;
 
 namespace ModelContextProtocol.Tests;
 
-public class SseServerIntegrationTests : IClassFixture<SseServerIntegrationTestFixture>
+public class SseServerIntegrationTests : LoggedTest, IClassFixture<SseServerIntegrationTestFixture>
 {
     private readonly SseServerIntegrationTestFixture _fixture;
 
-    public SseServerIntegrationTests(SseServerIntegrationTestFixture fixture)
+    public SseServerIntegrationTests(SseServerIntegrationTestFixture fixture, ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _fixture = fixture;
+        _fixture.Initialize(testOutputHelper);
     }
 
     private Task<IMcpClient> GetClientAsync(McpClientOptions? options = null)
@@ -17,7 +20,7 @@ public class SseServerIntegrationTests : IClassFixture<SseServerIntegrationTestF
         return McpClientFactory.CreateAsync(
             _fixture.DefaultConfig,
             options ?? _fixture.DefaultOptions,
-            loggerFactory: _fixture.LoggerFactory);
+            loggerFactory: LoggerFactory);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Transport/SseClientTransportTests.cs

@@ -1,5 +1,4 @@
-using Microsoft.Extensions.Logging.Abstractions;
+using ModelContextProtocol.Configuration;
-using ModelContextProtocol.Configuration;
 using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Transport;
 using ModelContextProtocol.Tests.Utils;
@@ -8,12 +7,13 @@ using System.Reflection;
 
 namespace ModelContextProtocol.Tests.Transport;
 
-public class SseClientTransportTests
+public class SseClientTransportTests : LoggedTest
 {
     private readonly McpServerConfig _serverConfig;
     private readonly SseClientTransportOptions _transportOptions;
 
-    public SseClientTransportTests()
+    public SseClientTransportTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _serverConfig = new McpServerConfig
         {
@@ -39,7 +39,7 @@ public class SseClientTransportTests
     public async Task Constructor_Should_Initialize_With_Valid_Parameters()
     {
         // Act
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, LoggerFactory);
 
         // Assert
         Assert.NotNull(transport);
@@ -58,21 +58,21 @@ public class SseClientTransportTests
     [Fact]
     public void Constructor_Throws_For_Null_Options()
     {
-        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(null!, _serverConfig, NullLoggerFactory.Instance));
+        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(null!, _serverConfig, LoggerFactory));
         Assert.Equal("transportOptions", exception.ParamName);
     }
 
     [Fact]
     public void Constructor_Throws_For_Null_Config()
     {
-        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, null!, NullLoggerFactory.Instance));
+        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, null!, LoggerFactory));
         Assert.Equal("serverConfig", exception.ParamName);
     }
 
     [Fact]
     public void Constructor_Throws_For_Null_HttpClientg()
     {
-        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, _serverConfig, null!, NullLoggerFactory.Instance));
+        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, _serverConfig, null!, LoggerFactory));
         Assert.Equal("httpClient", exception.ParamName);
     }
 
@@ -81,7 +81,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
 
         bool firstCall = true;
 
@@ -109,7 +109,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
         var tcsConnected = new TaskCompletionSource();
         var tcsDone = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
         var callIndex = 0;
@@ -157,7 +157,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
 
         var retries = 0;
         mockHttpHandler.RequestHandler = (request) =>
@@ -177,7 +177,7 @@ public class SseClientTransportTests
     [Fact]
     public async Task SendMessageAsync_Throws_Exception_If_MessageEndpoint_Not_Set()
     {
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, LoggerFactory);
 
         // Assert
         await Assert.ThrowsAsync<InvalidOperationException>(() => transport.SendMessageAsync(new JsonRpcRequest() { Method = "test" }, CancellationToken.None));
@@ -188,7 +188,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
 
         var firstCall = true;
         mockHttpHandler.RequestHandler = (request) =>
@@ -227,7 +227,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
 
         var firstCall = true;
         mockHttpHandler.RequestHandler = (request) =>
@@ -266,7 +266,7 @@ public class SseClientTransportTests
     {
         using var mockHttpHandler = new MockHttpHandler();
         using var httpClient = new HttpClient(mockHttpHandler);
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, LoggerFactory);
 
         var callIndex = 0;
         mockHttpHandler.RequestHandler = (request) =>
@@ -303,7 +303,7 @@ public class SseClientTransportTests
     [Fact]
     public async Task CloseAsync_Should_Dispose_Resources()
     {
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, LoggerFactory);
 
         await transport.CloseAsync();
 
@@ -313,7 +313,7 @@ public class SseClientTransportTests
     [Fact]
     public async Task DisposeAsync_Should_Dispose_Resources()
     {
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, NullLoggerFactory.Instance);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, LoggerFactory);
 
         await transport.DisposeAsync();
 

tests/ModelContextProtocol.Tests/Transport/StdioServerTransportTests.cs

@@ -1,8 +1,8 @@
-using Microsoft.Extensions.Logging.Abstractions;
+using ModelContextProtocol.Protocol.Messages;
-using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Transport;
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Server;
+using ModelContextProtocol.Tests.Utils;
 using ModelContextProtocol.Utils.Json;
 using System.IO.Pipelines;
 using System.Text;
@@ -10,11 +10,12 @@ using System.Text.Json;
 
 namespace ModelContextProtocol.Tests.Transport;
 
-public class StdioServerTransportTests
+public class StdioServerTransportTests : LoggedTest
 {
     private readonly McpServerOptions _serverOptions;
 
-    public StdioServerTransportTests()
+    public StdioServerTransportTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
     {
         _serverOptions = new McpServerOptions
         {
@@ -68,7 +69,7 @@ public class StdioServerTransportTests
             _serverOptions.ServerInfo.Name,
             new Pipe().Reader.AsStream(),
             output,
-            NullLoggerFactory.Instance);
+            LoggerFactory);
             
         await transport.StartListeningAsync(TestContext.Current.CancellationToken);
         
@@ -122,7 +123,7 @@ public class StdioServerTransportTests
             _serverOptions.ServerInfo.Name,
             input,
             Stream.Null,
-            NullLoggerFactory.Instance);
+            LoggerFactory);
             
         await transport.StartListeningAsync(TestContext.Current.CancellationToken);
         
@@ -165,7 +166,7 @@ public class StdioServerTransportTests
             _serverOptions.ServerInfo.Name, 
             new Pipe().Reader.AsStream(),
             output, 
-            NullLoggerFactory.Instance);
+            LoggerFactory);
             
         await transport.StartListeningAsync(TestContext.Current.CancellationToken);
         

tests/ModelContextProtocol.Tests/Utils/LoggedTest.cs

@@ -0,0 +1,18 @@
+using Microsoft.Extensions.Logging;
+using ModelContextProtocol.Test.Utils;
+
+namespace ModelContextProtocol.Tests.Utils;
+
+public class LoggedTest(ITestOutputHelper testOutputHelper)
+{
+    public ITestOutputHelper TestOutputHelper { get; } = testOutputHelper;
+    public ILoggerFactory LoggerFactory { get; } = CreateLoggerFactory(testOutputHelper);
+
+    private static ILoggerFactory CreateLoggerFactory(ITestOutputHelper testOutputHelper)
+    {
+        return Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        {
+            builder.AddProvider(new XunitLoggerProvider(testOutputHelper));
+        });
+    }
+}

tests/ModelContextProtocol.Tests/Utils/XunitLoggerProvider.cs

@@ -0,0 +1,52 @@
+using System.Globalization;
+using System.Text;
+using Microsoft.Extensions.Logging;
+
+namespace ModelContextProtocol.Test.Utils;
+
+public class XunitLoggerProvider(ITestOutputHelper output) : ILoggerProvider
+{
+    public ILogger CreateLogger(string categoryName)
+    {
+        return new XunitLogger(output, categoryName);
+    }
+
+    public void Dispose()
+    {
+    }
+
+    private class XunitLogger(ITestOutputHelper output, string category) : ILogger
+    {
+        public void Log<TState>(
+            LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
+        {
+            var sb = new StringBuilder();
+
+            var timestamp = DateTimeOffset.UtcNow.ToString("s", CultureInfo.InvariantCulture);
+            var prefix = $"| [{timestamp}] {category} {logLevel}: ";
+            var lines = formatter(state, exception);
+            sb.Append(prefix);
+            sb.Append(lines);
+
+            if (exception is not null)
+            {
+                sb.AppendLine();
+                sb.Append(exception.ToString());
+            }
+
+            output.WriteLine(sb.ToString());
+        }
+
+        public bool IsEnabled(LogLevel logLevel) => true;
+
+        public IDisposable BeginScope<TState>(TState state) where TState : notnull
+            => new NoopDisposable();
+
+        private sealed class NoopDisposable : IDisposable
+        {
+            public void Dispose()
+            {
+            }
+        }
+    }
+}