Refactor tests

[nezlobnaya]

Using t.Setenv instead of os.Setenv in tests provides a safer and more controlled way to manage environment variables during test runs. The t.Setenv method automatically restores the original environment variables at the end of the test, preventing potential pollution of the global environment state that could affect other tests.
Ensure os.Args is restored after modification to prevent test pollution. Restoring os.Args helps maintain isolation between tests, ensuring that each test starts with a clean state.