The lunge test is a weightbearing measurement of the static range of motion of the ankle joint that has been shown to have good reliability and a limitation in it has been associated with an increased risk for some injuries.
To do a lunge test, you have you have the patient place the foot perpendicular to a wall and then lunge with the knee towards the wall. The foot is progressively moved away from the wall until the maximum range of dorsiflexion is reached without the heel leaving the ground. You can then measure the distance of the foot from the wall or the angle of the tibial shaft to vertical.
Measuring the ankle of the tibia is preferable as the distance of the foot to the wall will be affected by the height of the patient.
It is also a good idea to also do the lunge test in shoes (with and without foot orthotics if they have them) to see what influence they have on the range of motion.