Fresh Chocolate is usually shiny and smooth on the surface of the Chocolate and has a good texture to it.
Chocolate that is going bad will usually develop cracks and become rough on the surface and may even start to turn white.
The chocolate is basically just going stale and doesn't mean it's bad to eat or unsafe to eat although it just doesn't taste as good.
Most Chocolate stays fresh for around 6 to 7 months before it begins to go bad.
I've eaten old chocolate that I've kept for a year or 2 and it's still been safe to eat but just doesn't taste as good.
However if the chocolate has gone bad to the point of it making you sick then it will likely smell bad or maybe mold will be growing on it.
As long as the chocolate smells good or okay and there's no mold growth on the chocolate it's safe to eat.