add basic tests for the dart mcp-server command

Change-Id: I7c6071fc7b015f8d7e0cbdf4b2cb2d31358d442c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/437140
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Ben Konyi <[email protected]>
Auto-Submit: Jake Macdonald <[email protected]>

Author: jakemac53

pkg/dartdev/pubspec.yaml

@@ -43,6 +43,7 @@ dependencies:
 
 # Use 'any' constraints here; we get our versions from the DEPS file.
 dev_dependencies:
+  dart_mcp: any
   expect: any
   lints: any
   pub_semver: any

pkg/dartdev/test/commands/mcp_server_test.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:dart_mcp/client.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('dart mcp-server', () {
+    test('can be connected with a client', () async {
+      final client = TestMCPClient();
+      addTearDown(client.shutdown);
+      final serverConnection = await client.connectStdioServer(
+          Platform.resolvedExecutable,
+          ['mcp-server', '--experimental-mcp-server']);
+      final initializeResult = await serverConnection.initialize(
+          InitializeRequest(
+              protocolVersion: ProtocolVersion.latestSupported,
+              capabilities: client.capabilities,
+              clientInfo: client.implementation));
+
+      expect(initializeResult.protocolVersion, ProtocolVersion.latestSupported);
+      serverConnection.notifyInitialized();
+
+      expect(
+        await serverConnection.listTools(ListToolsRequest()),
+        isNotEmpty,
+      );
+    });
+
+    test('requires the --experimental-mcp-server flag', () async {
+      final processResult =
+          await Process.run(Platform.resolvedExecutable, ['mcp-server']);
+      expect(processResult.exitCode, isNot(0));
+      expect(processResult.stderr,
+          contains('Missing required flag --experimental-mcp-server'));
+    });
+  });
+}
+
+base class TestMCPClient extends MCPClient {
+  TestMCPClient()
+      : super(Implementation(name: 'test client', version: '0.1.0'));
+}