There can be situations where testers are forced to perofrm testing with no or less requirements.
Here are some of the possible solutions to such cases where it is lacking or missing documentations:
- By talking to relevant groups of people that may have more understanding of how the system/application works or should behave
- Error guessing testing technique could be used by the tester who is experienced with the system under test
- Exploratory testing could be carried out to learn more about the system. This would be usually time-boxed.