This is the Oxford diagnostic test. It has 3 levels of complexity, which in my experience are relatively consistent with our levels. Note, however, that a couple of questions maybe confusing for students as this is aimed at British learners. LINK
That’s why pro bono work is great. You choose to do it, and if you’re choosing to do it to grow your own work, your deal is essentially that you’re not going to collaborate. You’re going to do the job the way you think the job is gonna be done.