Willpower is an important skill to have. A simple test of willpower is not scratching an itch until it goes away. This one should only torment you a mild amount.
A true test of willpower is depriving yourself of any and all "useless" activities for as long as possible. Most easy sources of dopamine will fall into this category. Things such as mindlessly browsing social media pages, watching random YouTube videos, gaming, and other similar activities.
I've never done drugs, but I'd assume quitting that should be significantly harder.
Thus if you fail to even last a day, you better not even dream of going near any drugs.
If you last much longer, you obviously have enough willpower to never touch drugs.