Add client conformance tests (#1102)

Co-authored-by: Stephen Halter <halter73@gmail.com>

tests/Common/Utils/NodeHelpers.cs

@@ -0,0 +1,70 @@
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+
+namespace ModelContextProtocol.Tests.Utils;
+
+/// <summary>
+/// Helper utilities for Node.js and npm operations.
+/// </summary>
+public static class NodeHelpers
+{
+    /// <summary>
+    /// Creates a ProcessStartInfo configured to run npx with the specified arguments.
+    /// </summary>
+    /// <param name="arguments">The arguments to pass to npx.</param>
+    /// <returns>A configured ProcessStartInfo for running npx.</returns>
+    public static ProcessStartInfo NpxStartInfo(string arguments)
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            // On Windows, npx is a PowerShell script, so we need to use cmd.exe to invoke it
+            return new ProcessStartInfo
+            {
+                FileName = "cmd.exe",
+                Arguments = $"/c npx {arguments}",
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                UseShellExecute = false,
+                CreateNoWindow = true
+            };
+        }
+        else
+        {
+            // On Unix-like systems, npx is typically a shell script that can be executed directly
+            return new ProcessStartInfo
+            {
+                FileName = "npx",
+                Arguments = arguments,
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                UseShellExecute = false,
+                CreateNoWindow = true
+            };
+        }
+    }
+
+    /// <summary>
+    /// Checks if Node.js and npx are installed and available on the system.
+    /// </summary>
+    /// <returns>True if npx is available, false otherwise.</returns>
+    public static bool IsNpxInstalled()
+    {
+        try
+        {
+            var startInfo = NpxStartInfo("--version");
+
+            using var process = Process.Start(startInfo);
+            if (process == null)
+            {
+                return false;
+            }
+
+            process.WaitForExit(5000);
+            return process.ExitCode == 0;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+}