As Andrew said, motoring is not the ideal test, unless you have a variable voltage available. Usually, if a generator will motor at 3-4V, it is OK.
I have a growler but never use it, I prefer to "voltage drop" the armatures.
In fact, there are people with growlers who don't have a clue how to use them properly and only test for short circuits, completely disregarding open circuits, which is the most common fault.
Then there are earth faults, uncommon, but again, disregarded.
Trev.