refactor/test integration

[mariangz]

Overview

Modernize the test suite: replace var with const / let, convert callbacks to async/await, and use arrow functions across all test files. No functional changes.

Testing recommendations

Related Issues or Pull Requests

Checklist

• I am not a bot
• This is my own work, I did not use AI, LLM's or similar technology for code or docs generation
• Code is written and works correctly
• Changes are covered by tests
• Documentation changes were made in the docs folder