ENGAGE

[When the cruise control function is active], it must [enable a set/accel button to lock in the current speed as the desired speed for the cruise control]. Additionally, there should be two buttons allowing the driver to increase or decrease the desired speed for the cruise control. The desired speed should be shown in the cockpit.

Test: Set a desired speed and check if the same speed is shown in the cockpit. Then, increase and decrease the speed using the speed buttons and do the same check again. Probably also measuring the speed of the car from the outside, just to be sure.