Has there ever been a situation where there is no documentation, but you need to test the functionality?

Yes, I have encountered situations where there is no documentation, but I need to test the functionality. In such cases, I use several approaches:

• Exploratory testing: I study the interface, try different scenarios to understand how the system should work.
• Analyzing requirements from other sources: I discuss with developers, business analysts, or clients to gather information about the functionality.
• Logging and debugging: I look at logs, the console to understand the system's behavior.
• Using analogies with similar functions or previous versions.

This approach helps identify main scenarios and create test cases even without formal documentation.