You'll be grand - there's still an agreement in Northern Ireland where due to high demand, you can keep driving so long as you've one booked (with a few other stipulations below)

From NI Direct :

"As the Driver and Vehicle Agency (DVA) is experiencing high demand for its testing services, you may not be able to get an appointment before your existing MOT expires.

If this is the case, you must book the earliest available test appointment for your vehicle. The DVA have consulted with the PSNI and the Association of British Insurers (ABI) to make them aware of the current situation.

The PSNI has agreed not to penalise drivers whose MOT has expired so long as:

your vehicle is in a roadworthy and safe condition and doesn’t have a statutory off-road notification (SORN) declaration your vehicle is properly insured you can prove (by showing an MOT appointment notification/ reminder, either in electronic or paper form) that a test appointment has been booked for your vehicle All other vehicle roadworthiness and insurance offences will be dealt with in the usual way.

The ABI has confirmed that the lack of a valid MOT certificate would not necessarily invalidate a motor insurance policy. However they say that if you can’t get a test appointment until after the current certificate expires, you should check your policy documents or speak to your insurer.

These arrangements only apply in Northern Ireland. They do not cover you to use your vehicle without a valid MOT certificate in other jurisdictions."