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

@@ -4290,4 +4290,58 @@ describe("elicitInput()", () => {
       text: "No booking made. Original date not available."
     }]);
   });
+
+  /**
+   * Test: Tool parameter validation with incorrect capitalization
+   * This test demonstrates that tools currently silently ignore unknown parameters,
+   * including those with incorrect capitalization. This should fail to show the issue exists.
+   */
+  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",
+    });
+
+    // Register a tool that expects optional 'userName' and 'itemCount'
+    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),
+    ]);
+
+    // Call the tool with unknown parameters (incorrect capitalization)
+    // These should be rejected but currently aren't - they're silently ignored
+    const result = await client.request(
+      {
+        method: "tools/call",
+        params: {
+          name: "test-strict",
+          arguments: { username: "test", itemcount: 42 }, // Should be rejected as unknown parameters
+        },
+      },
+      CallToolResultSchema,
+    );
+
+    // This expectation should fail because the tool currently accepts the call
+    // and silently ignores unknown parameters, returning success instead of error
+    expect(result.isError).toBe(true);
+    expect(result.content[0].text).toContain("Invalid arguments");
+  });
 });