Let's say I want to grow a new hybrid strain of lawn grass. What's the best way make sure the seeds are viable?

Plant them.

Did they grow? Yes=viable.

Happy to help :)

Adding water

Expose them to a few seconds of audio from a right-wing podcast: if they roll away from the speakers, they're viable, if they stay still they're non-viable, and if they roll Towards the speaker, they're Triffid seeds, and should be killed with fire.