Add Unit Tests for Authentication

[Durgesh4993]

Description

Write unit tests to verify that user registration, login, and authentication features work as expected.

Steps to Implement

1. Set up a testing framework such as jest or mocha.
2. Write tests for user registration and login functionality to ensure that:
   • A valid user can register and log in.
   • An invalid user gets an error response.
3. Ensure that JWT authentication works by testing protected routes.

Expected Outcome

All authentication features are covered by unit tests, ensuring the system behaves as expected.