Yes, but as I said in a previous post, the guardia won´t say anything if you show them the booking for the next test, as they realise that it is very difficult to get one for the day it expires.
I also mentioned that as from next year, 2017, drivers will have 30 days grace after the expiry date to get the vehicle tested.
Really, the problem doesn´t lie with the authorities but with the insurance companies. If you are involved in an accident, the company will always reimburse the other party, but could, if they felt like it, sue you for this money if they considered that the accident was caused due to the vehicle being in a bad state of repair, something the ITV would, presumably, have spotted first and would have obliged the owner of the vehicle to put right.
In other words, no ITV, no insurance coverage (in theory) .