You can try a tetrazolium test:

Germinate your seeds on a moist filter paper with the mixed adsorbent at whatever rate you think is appropriate for your conditions, for sufficient time to ensure the seeds have broken dormancy (I used 72 h for Vitis seeds).

Cut seeds open with a suitable blade/scalpel etc, and lay them cut side down on a filter paper soaked in 2,3,5 triphenyltetrazolium chloride 1g/100ml for 48 h. Red formazan deposits in the endosperm indicate viable seeds.

From MACKAY, D. B.; 1972: The measurement of viability. In: E. H. ROBERTS

(Ed.): Viability of Seeds, 172-208. Chapman and Hall, London.

There may be other tests out there worth trying.