Add Unit Tests for All API Endpoints

[Hayk Davtyan]

Is your feature request related to a problem? Please describe.
We need to add unit tests to ensure the reliability and correctness of all API endpoints. This will help catch bugs early and maintain the quality of our codebase.

Describe the solution you'd like
Use a testing framework like unittest, pytest, or nose.

Describe alternatives you've considered
N/A

Additional context

• All API endpoints have corresponding unit tests.
• Tests cover all critical paths, edge cases, and error handling.
• Tests are run automatically as part of the CI/CD pipeline.
• Code coverage meets the project's standards (e.g., 80%+).