fix unit tests

src/middleware/multer.middleware.test.ts

@@ -1,5 +1,5 @@
 // src/middleware/multer.middleware.test.ts
-import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach, Mock } from 'vitest';
 import multer from 'multer';
 import type { Request, Response, NextFunction } from 'express';
 import { createUploadMiddleware, handleMulterError } from './multer.middleware';