Not your average rhubarb jam

"It's always important to do a quick jam test before you stop cooking your jams. What is a jam test? At the end of the suggested cooking time, place a small spoonful of the hot jam on a cold plate (preferably from the freezer), then hold the plate at an angle. If the jam runs easily down the plate, the jam needs more time to cook. If the mass becomes solid after a short time and you can run your finger through the jam leaving two unconnected sides, the jam test has been passed and you're ready to put the jam in jars."