Germination is a clear sign that the seeds still have the capacity to grow. If more than half of your tested seeds germinate, this indicates that the batch is partially viable.
A success rate of 80% or higher means your seeds have excellent viability. Another technique is to soak the seeds in a jar of lukewarm water (around 30°C) for a few hours. This process also helps soften the outer seed coat, making it easier to germinated. The foolproof tip: the germination test with paper towel.