Keep in mind that this is a very course troubleshooting method that detects "broken" stuff and not items that are working, but not quite up to speed.
Audio signals to the speakers are AC. So, a basic multimeter will measure the audio signal. If you have a driver that is "quiet" there should be a presence of AC at the driver terminals iF the signal is arriving from the crossover. Just put any static signal (pink noise, or test tone) at the speakers input terminals and you should have some value there. If not, you most likely have a problem upstream somewhere. If this is the case, you can also inject the signal from a test amp (small amp/receivers work well for this) and inject signal directly to the raw driver as an additional test. Make sure the speaker is disconnected from your main amp. In the case of a tweeter, you may want to connect a capacitor (4-7uF) inline just to be safe. If the raw driver plays, you have a working driver, not necessarily a optimum driver, but a working driver.
I’m not an engineer, but have used this method for some time.