Throw it out on fuzzy mould of any kind, on water sitting in it, or on a smell that is sharp and sour rather than strong and savoury. Fats go rancid with moisture, light, heat and air, and a cupboard in a warm kitchen is more of those than people think.
Clean dry jars, sealed tight, somewhere cool and dark for shorter keeping, and the fridge if you are making six weeks' worth at a time. Yours may well be fine; the spoon test will settle it faster than any of us can.