TestSys() sends the '*TST?' message to all the devices in the addressList array, then reads their responses into the results array. This will cause devices that conform to the IEEE 488.2 standard to perform a self-test and respond with a zero on success. A non-zero response indicates an error during the self-test.
The number of devices which responded with nonzero values from their self-tests is returned in ibcnt and ibcntl. If a device fails to respond to the *TST? query, an error will be flagged in ibsta (this is different than NI's documented behaviour which is broken).