That varies too much for me to estimate. For instance, I have not tested at all in several weeks, so my average has been pulled way down. Well, I'd better not. I'll let the authors tell about them if they wish. I think the question you really wanted to ask me is if I noticed any times of the year when testing requests reach a peak.
Releases come after testing, of course.
The competition has skewed this because more authors are focusing their energies on it. Otherwise, I would say I get more requests in late February and early March than at any other time. I get the fewest requests from October through January. Again, the competition affects this. Last year, counting competition and full-size games, I had eight going at once.