You can use the seed flotation test to differentiate between healthy, insect-infested, or otherwise damaged seeds; it provides a complement to the cut test or tetrazolium staining test since incising would destroy the seeds. Seeds that sink in water are deemed to have healthy embryos, whereas those that float are assumed to be unsound. Although the true viability of the embryo cannot be assessed by this method, it does differentiate between sound seeds and those with a reduced probability of germination.

From my paper in press: Size-based fruit selection by a keystone avian frugivore and effects on seed viability, 10.1080/0028825X.2016.1247882.

Andrew :-) 

Also, the ‘cut test’, or visual examination of the exposed surface (or embryo) of unimbibed seeds under magnification, can be used. The cut test is as reliable as tetrazolium staining techniques. Cut the seed coat and seed and expose the embryo, and examine using an 8× magnifier. Seeds are considered to be unsound if the embryo is absent, ‘mushy’, dehydrated, ‘powdery’ (or friable), grossly discolored (i.e. not glistening white), malformed, has large cavities, or if there is obvious animal (insect or mammal) damage. 

And, of course, you can germinate the seeds!

Also from my paper in press: Size-based fruit selection by a keystone avian frugivore and effects on seed viability, 10.1080/0028825X.2016.1247882.

Andrew :-)