Take your seeds and put them in a container of water. If the seeds sink, they will most likely remain viable. If they float, they probably won't sprout. Just use the feel of touch.
Place the seed between your thumb and forefinger and squeeze it. Young, healthy seeds will feel firm and will not give in to pressure. Older seeds may feel a little soft, and old, dry seeds may even crumble or crack, as they lack the moisture and nutrient content of younger specimens. A standard germination test can be performed on older seeds using paper towel germination and sachet testing.
This is one of the most common methods for testing seed viability. This is the easiest method. Simply place the seeds in a cup, jar, or bucket of water and let them soak. Bad seeds will continue to float indefinitely, while good seeds will sink in a few hours.
Marijuana seeds from the same plant, even from the same flower, can also have different visual characteristics. Performing a seed viability test is really the only reliable way to know if seeds are viable. Yes, I bet freezing seeds helps preserve their viability, and it definitely adds the element of cold stratification for seeds that need it. There is still a huge discrepancy between the quality of cannabis seeds from a reputable seed bank and those found at the bottom of a mediocre marijuana bag.
But if the seeds are more than two years old, you should consider doing one of these three reliable seed germination tests before planting your garden. Larger caliber marijuana seeds have better germination rates, better genetics and better yields. When you're done with the seed viability test, you can plant the seeds that germinated if you want. If your germination rate is less than 60%, consider buying new seeds or planting them more densely to compensate for the low germination rate.
If you like to store seeds from your garden, or have a lot of old seeds lying around, take the time to do this simple germination test on them. As I said earlier, make sure to give it a couple of weeks to allow slower seeds to germinate before you give up your seed viability testing efforts. But I wouldn't use less than five seeds, otherwise your seed viability test wouldn't be very accurate. Other times it's because seeds lose their viability over time and many types of old seeds don't germinate.
Although cannabis seeds don't have such extreme longevity, growers tend to be successful growing seeds from two or three seasons ago.