This question is to test your general approach to work and see if you fit our culture.
Your boss is always going to find a fault, so when given a new task do you:-
a) Complete the job as best you can, knowing that a fault will be found, you will be castigated, but at least you did your best.
b) Do the job as quickly (and as slack) as possible, knowing that a fault will be found but at least you will have the time to fix it.
c) Do the job well, but leave some faults that are easy to find to keep QA happy.
d) Start the job but get your updated CV out there immediately.