Sorry minor side step - Wasn't it re calibration (maintanence miss-rigging)of the trim wheel settings that led to the violent aerobatics on the Ezy 737 test flight over the east coast last year? 19000ft a min decent at one point!
More likely a manual reversion test. Done after maint on the elevator syst. Turn flt ctl power off. The a/c should continue to fly level. If it doesn't log how much trim is needed and it gets adjusted again. It's not mis rigging it's a rigging check. Adjustment is often needed.