Currently there is no certification or aptitude aimed at testing a politician's preparedness for the occupation, yet we require that engineers and lawyers to take such exams. Politicians have similarly important and far-reaching roles in society, so such an exam would be appropriate. Whether it be a one-time test upon entry into a new office or a periodic re-certification (like the LEED examanations), this would help ensure that politicians are well-qualified.
Here is a list of occupations that currently require certification:
http://en.wikipedia.org/wiki/Professional_certification#Areas_of_certifi...