This read-write object reports and controls the state of this self-test: ready (not running), test (requested to start), or testing (currently in progress). Admins begin a test by writing test(2) to this object, then poll it until the value transitions from testing(3) back to ready(1) to know the test has completed. For example, an admin troubleshooting a suspected hardware fault sets diagTestStatus to test(2) to initiate that specific self-test, then polls the object until it returns to ready(1) to see the test has finished.