Fix parallel integration test server startup

CONTRIBUTING.md

@@ -26,6 +26,9 @@ Before you begin, ensure you have the following installed:
 - **.NET SDK 10.0 or later** - Required to build and test the project
   - Download from [dotnet.microsoft.com/download](https://dotnet.microsoft.com/download)
   - Verify installation: `dotnet --version`
+- **Node.js 22 or later and npm** - Required for integration and conformance tests
+  - Run `npm ci` from the repository root before running tests to install the pinned test dependencies.
+  - Integration tests launch the installed servers directly with `node`, avoiding npm installation and shared-cache access during parallel tests.
 
 The dev container configuration in this repository includes all the necessary tools and SDKs to get started quickly.
 

tests/Common/Utils/NodeHelpers.cs

@@ -31,6 +31,20 @@ private static string FindRepoRoot()
         throw new InvalidOperationException("Could not find repository root (no package-lock.json found in ancestor directories).");
     }
 
+    /// <summary>
+    /// Gets the entry point of a test server installed by 'npm ci', without invoking npm during tests.
+    /// </summary>
+    public static string GetTestServerScriptPath(string serverName)
+    {
+        var scriptPath = Path.Combine(FindRepoRoot(), "node_modules", "@modelcontextprotocol", $"server-{serverName}", "dist", "index.js");
+        if (!File.Exists(scriptPath))
+        {
+            throw new FileNotFoundException("Test server is not installed. Run 'npm ci' from the repository root before running tests.", scriptPath);
+        }
+
+        return scriptPath;
+    }
+
     /// <summary>
     /// Ensures npm dependencies are installed by running 'npm ci' from the repo root.
     /// This is safe to call multiple times; it only runs once per test process.

tests/ModelContextProtocol.Tests/ClientIntegrationTestFixture.cs

@@ -16,15 +16,16 @@ public class ClientIntegrationTestFixture
 
     public ClientIntegrationTestFixture()
     {
-        const string ServerEverythingVersion = "2026.1.26";
         string testServerExecutable = Path.Combine(AppContext.BaseDirectory, "TestServer.exe");
         string testServerDll = Path.Combine(AppContext.BaseDirectory, "TestServer.dll");
 
         EverythingServerTransportOptions = new()
         {
-            Command = "npx",
-            // Change to Arguments = ["mcp-server-everything"] if you want to run the server locally after creating a symlink
-            Arguments = ["-y", "--verbose", $"@modelcontextprotocol/server-everything@{ServerEverythingVersion}"],
+            Command = "node",
+            // To use a local Everything server, build it, then run `npm link <path-to-server-everything>`
+            // from this repository root after `npm ci`. The linked package must contain dist/index.js;
+            // no argument changes are needed because this path resolves through the package link.
+            Arguments = [NodeHelpers.GetTestServerScriptPath("everything")],
             Name = "Everything",
         };
 
@@ -36,7 +37,6 @@ public ClientIntegrationTestFixture()
 
         if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
         {
-            // Change to Arguments to "mcp-server-everything" if you want to run the server locally after creating a symlink
             TestServerTransportOptions.Arguments = [PlatformDetection.IsMonoRuntime ? testServerExecutable : testServerDll];
         }
     }

tests/ModelContextProtocol.Tests/ClientIntegrationTests.cs

@@ -61,6 +61,18 @@ public async Task Connect_ShouldProvideServerFields(string clientId)
         Assert.Null(client.SessionId);
     }
 
+    [Theory]
+    [MemberData(nameof(GetClients))]
+    public async Task ConnectConcurrently_Stdio(string clientId)
+    {
+        await Task.WhenAll(Enumerable.Range(0, 4).Select(async _ =>
+        {
+            await using var client = await _fixture.CreateClientAsync(clientId);
+            var tools = await client.ListToolsAsync(cancellationToken: TestContext.Current.CancellationToken);
+            Assert.NotEmpty(tools);
+        }));
+    }
+
     [Theory]
     [MemberData(nameof(GetClients))]
     public async Task ListTools_Stdio(string clientId)
@@ -464,8 +476,8 @@ public async Task CallTool_Stdio_MemoryServer()
         // arrange
         StdioClientTransportOptions stdioOptions = new()
         {
-            Command = "npx",
-            Arguments = ["-y", "@modelcontextprotocol/server-memory"],
+            Command = "node",
+            Arguments = [NodeHelpers.GetTestServerScriptPath("memory")],
             Name = "memory",
         };