Glow plug test is very simple!
They will feel warm to hot just after a cycle and this while still in place.
While being 'cycled' the glow plug buss bar reading will be somewhere around 9 volts due to the high current draw.
If so then fuel delivery is the next issue to check with bleeding the most probable 'cure'.
I like to bleed right up at each injector by simply cracking the fitting until I get a fuel leak.
While best to bleed each injector, doing only one will get mine to put-put stutter for a bit and then roar on all 3 cylinders shortly.