I would bet that this forum:
https://www.zero-forum.com/
has some documentation of any built-in testing the system itself can do.
This is another
https://www.electricmotorcycleforum.com/boards/index.php?board=35.0
I've never visited either one, other than some google searches now and then, so I don't know for sure what info they have.
To test the battery itself outside the system, it depends on exactly what you want to test for, as to what you would have to do.
If just doing a capacity/range test, the simplest way is to fully charge the bike, then ride it under the conditions you expect to encounter in your everyday usage until it says it is near-empty. The range you get in that test would be about the range you would typically get (this range will decrease by a bit every ride, possibly nearly unnoticeably, depends on the age and health of the battery itself and the actual usage).
Otherwise you'd need a test load sufficient to draw as much power from the battery as the bike would, and a way to "turn on" the battery (assuming it doesn't just output power without being connected to the bike, which it might not do if it has a safety feature for this), and a "wattmeter" or coulomb-meter to test the battery's capacity (Ah / Wh) and voltage drop under a load equivalent to what the bike would put it under during typical usage. Then compare the readings from the meter to what the specs Zero gave the battery when new, and see if the difference is acceptable to you.
You can also use those readings to guesstimate range, based on others' reports of Wh/mile or Wh/km usage for their Zeros of the same model under similar riding conditions to yours.