I've seen six months work - that's time enough to ramp up somewhat and deliver. In that regard, it's plenty of time to assess the traits that we're looking for in strong developers.
That is the usual practice in countries like France, where new hires are on a trial basis for a period of one to six months (all other things being equal, the trial period only means that both the employee and the employer may terminate the contract at the end of the period with minimal administrative fuss).
Do you get back to them with the decision well before the end of the period, though, or do you just leave them without an income at the end of it if you decide you don't want to hire them?
