[masraum]

The only test that I'm aware of is having someone start the car and watching the voltage. Unfortunately that's not a test of "the starter", it's a test of "the system." The system is the battery, cables, starter, and potentially even the motor itself.

If the voltage drops too low during starting, that could be a bad or going-bad battery (too few CCA/CA). It could also be a going-bad starter (too much draw), or bad cables or connections (insufficient current getting to the starter).