Kick off the SDK based on Symfony's MCP SDK

tests/Message/ErrorTest.php

@@ -0,0 +1,52 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Message;
+
+use Mcp\Message\Error;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Small;
+use PHPUnit\Framework\TestCase;
+
+#[Small]
+#[CoversClass(Error::class)]
+final class ErrorTest extends TestCase
+{
+    public function testWithIntegerId(): void
+    {
+        $error = new Error(1, -32602, 'Another error occurred');
+        $expected = [
+            'jsonrpc' => '2.0',
+            'id' => 1,
+            'error' => [
+                'code' => -32602,
+                'message' => 'Another error occurred',
+            ],
+        ];
+
+        $this->assertSame($expected, $error->jsonSerialize());
+    }
+
+    public function testWithStringId(): void
+    {
+        $error = new Error('abc', -32602, 'Another error occurred');
+        $expected = [
+            'jsonrpc' => '2.0',
+            'id' => 'abc',
+            'error' => [
+                'code' => -32602,
+                'message' => 'Another error occurred',
+            ],
+        ];
+
+        $this->assertSame($expected, $error->jsonSerialize());
+    }
+}