If you’re considering taking a Microsoft exam, you might be interested in Microsoft Certification Booster Packs. They give you a practice test and/or four extra retakes in case you fail, which may be very helpful if you’re not sure what to expect from the exam, or if it’s quite hard.
The offer expires on 30th September 2016, therefore you shouldn’t hesitate for too long. Then you get six months to actually take the exams.
It’s applicable to Dynamics certifications, nevertheless people in comments complained that practice tests aren’t available for Dynamics AX exams. If you consider buying a booster pack for a Dynamics AX exam, it may be safer to take the one with four retakes rather than practice tests.