What is the correct method to check if a motorcycle clutch is slipping under load?

1. Ride in a high gear at low speed and open the throttle quickly; check if engine RPM rises faster than road speed
2. Place the motorcycle on the center stand, engage first gear, and verify if the rear wheel rotates
3. Pull the clutch lever in completely and check if you can push the motorcycle forward easily
4. Measure the free play at the clutch lever tip with a steel rule