The best test I've found for no-pectin gel is to put a few small plates in the fridge while you're making the jam. As the jam begins to thicken and starts to sheet, instead of drip, off of a big spoon, put a dab on one of the cold plates and let the jam cool to room temperature. Then draw a line with your finger through the jam. If the jam runs back together again, it needs more boiling. If the line stays then the jam is ready. Too much boiling means too sticky/thick of a jam. You can kind of rescue a jam that's boiled too much by adding a bit of water to it, but it's best to do it right the first time.