<human>: Using a throwaway account here

24 year old guy here. In March I resigned from a Warehouse Supervisor job I held for a year. The reason I resigned was because of the result of a random drug test I took. I take adderall recreationally sometimes, and its usually out of my system completely within 24 hours. My luck, I got a call from people not part of the company asking me if i was prescribed it and that my results came back positive. So, knowing I would be fired the next day, I showed up early and quickly wrote a resignation letter and effectively quit.  

Now, I've been working at my father's liquor store since then. It's not cutting it financially. 

My question is: on future applications, how do you recommend I answer the question of why I am no longer employed by that company. I want to turn this negative into a positive here. I gained valuable skills there, and have good relations with my former bosses, but I can't write "I resigned pending termination resulting from a random drug screening." I need advice on how to approach this both on paper and verbally if it were to come up in an interview.

Summarize the given text in a few sentences.
<bot>: Failed drug test after +1 year of employment, resigned in anticipation of being fired. Recommendations on how to spin this on a job application. Thanks.