I found a box of LAS-8500P half wave bridge interface drivers in my attic. How can I test them with a multimeter to see if they are any good?
Assuming used pulls or something like that, if you put your multimeter on diode range and test the outputs and inputs relative to ground and you see diode junctions there, it's "probably" good.
If they are brand new, they're probably good, period.
A more thorough test, even a simple functional test, is going to require building up a circuit similar to those in the datasheet and making measurements.