It is unlikely that the MoT process has caused your vehicle's loss of power, as the test does not involve any mechanical work or subject the vehicle to any stress over and above that which occurs in normal driving. It is more likely that the timing of the fault is coincidence, but will require some kind of inspection to determine the cause. It could be an issue with the ignition system, air intake or fuelling, any of which could cause the vehicle to be down on power. We would suggest taking it to an independent Mazda specialist who can examine the vehicle and give you a diagnosis.