You are hired as part of a team of external Penetration Testers to work for a company with a large enterprise network.

Penetration Test Plan: 

You are facing a client who is nervous about you basically "hacking" their system, this is the scenario, and while you cannot dictate exactly what will happen once the testing actually begins you should be able to formulate a good plan of action. 

All you are doing here is providing your plan of action, indicating what you believe are possible good tests to complete based off of your current knowledge.  Of course as you progress with the actual testing it is possible you could remove or add to your steps.

In the real world no one is going to just give access to their network, they will want to know what you plan and to know what your backup plans are if things go wrong.

This case study is just to provide you an opportunity to explain what you would do in a situation similar to this  one, where a client is asking you to provide guidance and potentially solutions.  You are not predicting what will happen, so much as providing courses of action.