It is ONE of the common scenarios where documentation is not PROPERLY available for all kind of test cases, but the REQUIREMENT has to fulfill and deliver the same to the client on time. In that case normally TESTER are following some client provided mail where describe all the requirements properly, if possible screenshots of the application where those parts of changes clearly mentioned, or some Mon or verbal telephonic discussion done with the client for understanding exact functionality of that changes which is enough for TESTING quickly and deliver the same in expected timeline.

It is one of the common scenarios where documentation is not properly available for all kind of test cases, but the requirement has to fulfill and deliver the same to the client on time. In that case normally tester are following some client provided mail where describe all the requirements properly, if possible screenshots of the application where those parts of changes clearly mentioned, or some Mon or verbal telephonic discussion done with the client for understanding exact functionality of that changes which is enough for testing quickly and deliver the same in expected timeline.