How to act when testing new functionality if there are no requirements or documentation?

If there are no requirements and documentation, when testing new functionality, you should:

• Conduct exploratory testing, studying the application's behavior intuitively.
• Communicate with developers, business analysts, or stakeholders to gather information about the purpose and expected behavior.
• Use analogies with similar functions or previous versions to understand the logic.
• Create test scenarios based on observations and identified patterns.
• Document the features and questions found for further clarification.

This approach helps identify main scenarios and potential defects without formal documentation.