I am very mean with seeds and keep them for a very long time. If it is important to germinate seeds by a certain time of year I test them for viability a few weeks before hand.
Just put a few seeds on damp kitchen paper in a 'tupperware' box and leave in the dark for a few days. Depending on the percentage that have germinated, I can decide whether or not to buy new seeds.
Oh yes, the ones that have germinated inevitably are put into some compost to be grown on. Waste not want not!