test: add failing test showing unknown parameters are silently ignored

  This test demonstrates the current issue where tools accept unknown
  parameters (e.g. incorrect capitalization) without validation errors.
  The test uses 'username' and 'itemcount' instead of the expected
  'userName' and 'itemCount' parameters, which should be rejected
  but currently aren't.

  This test is expected to fail until strict validation is implemented.

Author: Adam Bloomston

src/server/mcp.test.ts

@@ -4085,4 +4085,44 @@ describe('elicitInput()', () => {
             }
         ]);
     });
+
+    test('should fail: tool with incorrect parameter capitalization is not rejected', async () => {
+        const mcpServer = new McpServer({
+            name: 'test server',
+            version: '1.0'
+        });
+
+        const client = new Client({
+            name: 'test client',
+            version: '1.0'
+        });
+
+        mcpServer.registerTool(
+            'test-strict',
+            {
+                inputSchema: { userName: z.string().optional(), itemCount: z.number().optional() }
+            },
+            async ({ userName, itemCount }) => ({
+                content: [{ type: 'text', text: `${userName || 'none'}: ${itemCount || 0}` }]
+            })
+        );
+
+        const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+
+        await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
+
+        const result = await client.request(
+            {
+                method: 'tools/call',
+                params: {
+                    name: 'test-strict',
+                    arguments: { username: 'test', itemcount: 42 }
+                }
+            },
+            CallToolResultSchema
+        );
+
+        expect(result.isError).toBe(true);
+        expect(result.content[0].text).toContain('Invalid arguments');
+    });
 });