An easy test on the primary ignition circuit (points /condensor).
Test for input to the coil with your test light (I assume you have an early tractor, 6 volt positive battery ground) on the Negitive side terminal of the coil, the light should light and stay that way even when cranking the engine. If this is good then go to next step, if not check to see why you are losing power to the coil (bad connection?)
Next go to the Positive terminal (the wire going to the points) The light should go on and off as you are cranking the engine. The light will come on when the points are open (circuit is open) and the light will go off when the points are closed (direct circuit to ground, no power is left to light the test light).
If the light stays on then the points are not closing (direct circuit to ground) if the light does not light then the points are remaining closed or the ciruit /wiring is going direct to ground.
Repeat test and make corrections until the light flashes on and off (wire going to points) as you crank the engine. When the light goes off and on the coil will provide secondary spark to the spark plugs, check to see if you have spark out of the coil at this point.
Good Luck and post back with your results