(Free Sparring is called Jayoo Matsoki)
If you are a blue belt and above you will be expected to demonstrate free sparring, this is as you would expect to see at competitions.
As your belt grade gets higher, you should be demonstrating more flexibility and better stamina to be able keep going.
Don't forget, when grading it's not sportsman like to always be attacking your opponent, let them have a try at attacking you.
The examiner wants to see both of be able to attack and defend, otherwise they won't be able to mark you - and that means both of you will suffer with low marks!
(In a grading situation, you would not make ANY contact with your opponent, unless you have been told to do so by the instructor and you have full sparring equipment on.)