A door lock system has four states: Locked, Unlocked, Open, and Alarming. The specification states: entering the correct PIN in the Locked state unlocks it; pulling the handle in the Unlocked state opens it; closing the door in the Open state returns it to Unlocked; entering an incorrect PIN three times consecutively in the Locked state triggers the Alarming state. To achieve 0-switch coverage (covering every valid transition at least once), what is the MINIMUM number of test cases needed?