OTOH, it's in line with other character absences - our heroes tend to "attend conferences" and the like especially during quiet times (such as the one suggested at the very start of the episode, with Crusher doing bridge watches as a hobby rather than tending to massive casualties). It's sort of fun that no convoluted explanation for the absence is inserted this time...
Also, it does seem consistent with the division of responsibilities. Riker is always the one in charge of personnel matters. He would be the logical choice to be administering and "grading" the test. Only when the results were in and the promotion needed to happen would Picard get involved.