Increase backend test coverage for core services and controllers

[kmuwanga83]

📌 Problem

Test coverage for backend components is limited or unclear, which may lead to regressions.

🎯 Objective

Improve reliability by adding unit and integration tests.

✅ Tasks

• Add tests for:
  • service layer
  • controllers
  • authentication/security
• Ensure tests run using Maven
• Document how to run tests locally

🧪 Acceptance Criteria

• Tests run successfully with mvn test
• Core endpoints are covered
• Documentation includes test instructions

💡 Suggested Labels

backend, testing, help wanted