unit testing for interface

server.ts

@@ -120,7 +120,7 @@ app.use('/api/users', userRouter);
 // --- Error Handling and Server Startup ---
 
 // Basic error handling middleware
-app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
+app.use((err: Error, req: Request, res: Response, _next: NextFunction) => {
   // Check if the error is from the timeout middleware
   if (req.timedout) {
     // The timeout event is already logged by the requestLogger, but we can add more detail here if needed.
@@ -128,9 +128,8 @@ app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
     return;
   }
   logger.error('Unhandled application error:', { error: err.stack, path: req.originalUrl });
-  // The 'next' parameter is required for Express to identify this as an error-handling middleware.
-  // We log it here to satisfy the 'no-unused-vars' lint rule, as it's not called in this terminal handler.
-  // logger.info('Terminal error handler invoked. The "next" function is part of the required signature.', { next: String(next) });
+  // The 4-argument signature is required for Express to identify this as an error-handling middleware.
+  // We prefix `next` with an underscore to indicate it's intentionally unused, satisfying the linter.
   if (!res.headersSent) {
     res.status(500).json({ message: 'Something broke!' });
   }