What main problems did you encounter when testing the application?

The main problems when testing an application often relate to:

• Logic errors: incorrect data handling, wrong conditions.
• Dependency issues: incompatible library or environment versions.
• Performance issues: slow responses, memory leaks.
• Input/output errors: incorrect file or network operations.
• Insufficient test coverage: missed cases leading to bugs.

To address these, it is important to use logging, debugging, unit and integration tests, and analyze logs and metrics.