heya

Put it in neutral and set the tension as per the manual (+/- 15mm to 25mm deflection on the bottom of the chain halfway between the front and rear sprockets on the side stand) and tighten up the rear axle, If you have a rear stand or some way of getting the rear wheel off the ground, do it, then slowly rotate the rear wheel and see if the chain tension stays the same throughout the entire length of the chain. If the chain becomes tight and loose as the rear wheel is rotated then i'd say it's stuffed. If the tension stays the same over the whole chain generally it should be fine.

Another check is to pull one of the chain links wrapped over the rear sprocket away from the sprocket, the further it moves away from the sprocket the more worn the chain is.

Really worn chains will also snatch when you ride at the same speed, ditch it, as this motion will cost you more in the long run as it loads the rear wheel bearings and transmission up

I've seen more chains fail due to joining linkages failing then from wear.

If it is worn and you insist on using it remember to adjust it to suit the tightest part of the chain.

Cheers