The VO2MAX test will mostly be conducted on the treadmill. You'll be asked to run on a treadmill at an increasing pace while wearing a mask that measures your oxygen consumption. You'll then increase the pace and speed up to a point where you're no longer able to increase your oxygen consumption further which will conclude your test.
Typically the VO2MAX should take around 15 minutes to complete starting with a 3 minute warm up followed by a step-wise ramp-up every 2.5 minutes though this is subjective to every person.
If you have an upcoming VO2MAX test coming up, don't forget to dress in exercise clothes!