PER_CLASS

Attach once and reuse the devices for every test of the class; detach after the last one. Saves the driver start of each attach (about 1 s on an emulator, several on a slow phone) but nothing is reset between tests: the app keeps whatever state the previous test left, so each test must bring it where it needs it (coldLaunch(), clearData()). A reused device is probed before each test; one that stopped working (quarantined, driver lost) is detached and a fresh one attached. Failure artifacts are still captured per test.