L
I quess I was not clear on the "Test AMM"

What I mean is that one replaces the suspect AMM with a known GOOD one.
That now becomes a "TEST AMM TOOL "
It is just an easy way for quick diagnosis. Like changing a tail light bulb with a known good one to save the time of checking for voltage and ohmmeter-checking the bulb .
There is no AMM TEST TOOL. It is just a Tech trick of swapping the part with a known good one for testing purposes...
Techs usually have access to these, DIYers don't..
Unfortuately for diyers , AMM and MAF sensors are very hard to diagnose
without proper equipment..
But regulator test and looking around for vac leaks is easy and sometimes are the problem..