If the exogenous test in your blood stream exceeds the body's natural production, you will be on your way to totally shut down.
So, if your body produces around 7mg a day and for simplicity we use that number for a concentration in the blood example - taking more than 49mg per week will shut down natural production. It's an overly simplistic example, but none of the other factors are going to change the fact that you are going to be administring several times the body's natural test production and at that point it's all a wash.