Default draft protocol support: sessionless + handshake-less (SEP-2575 + SEP-2567) (#1610)

tests/ModelContextProtocol.Tests/Server/PingProtocolGatingTests.cs

@@ -0,0 +1,53 @@
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Client;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.Tests.Server;
+
+/// <summary>
+/// Verifies that the built-in <c>ping</c> handler is gated by protocol version.
+/// SEP-2575 (the draft 2026-07-28 revision) removes <c>ping</c>; servers must
+/// respond with <c>-32601 MethodNotFound</c>. Legacy protocol versions still
+/// support <c>ping</c> per the spec.
+/// </summary>
+public sealed class PingProtocolGatingTests : ClientServerTestBase
+{
+    public PingProtocolGatingTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper, startServer: false)
+    {
+    }
+
+    protected override void ConfigureServices(ServiceCollection services, IMcpServerBuilder mcpServerBuilder)
+    {
+    }
+
+    [Fact]
+    public async Task Ping_OnDraftSession_ReturnsMethodNotFound()
+    {
+        StartServer();
+        await using var client = await CreateMcpClientForServer(new McpClientOptions
+        {
+            ProtocolVersion = McpSession.DraftProtocolVersion,
+        });
+
+        var ex = await Assert.ThrowsAsync<McpProtocolException>(async () =>
+            await client.PingAsync(cancellationToken: TestContext.Current.CancellationToken));
+
+        Assert.Equal(McpErrorCode.MethodNotFound, ex.ErrorCode);
+    }
+
+    [Fact]
+    public async Task Ping_OnLegacySession_StillSucceeds()
+    {
+        // Default server config; client pinned to 2025-11-25.
+        StartServer();
+        await using var client = await CreateMcpClientForServer(new McpClientOptions
+        {
+            ProtocolVersion = "2025-11-25",
+        });
+
+        var result = await client.PingAsync(cancellationToken: TestContext.Current.CancellationToken);
+        Assert.NotNull(result);
+    }
+}