It depends on what state and country. Like in Colorado, USA there is already licensing instead of certification only. Every state is different.
It will also depend on how prepared you are academically, physically and mentally. Even if the examination is easy BUT you did not prepare for it, then you will really fail. Preparation is still the key. Just do your best and even if you failed, you have an edge when you retake the examination.
If you are about to make a decision to go back to school and choose massage/ spa therapy over other careers. You should read these to books:
Massage Therapy Career Guide by S. Capellini
Spa, Massage Therapy and Wellness Resource Book and Career Guide by E. Estipona
Hope this helps a little.