I recently started lead climbing in the gym after taking a lead climbing class. So far, I've only led with someone I know from the class who I watched lead belaying a number of times during the class. However, at some point I will want to lead climb with others and will therefore need a way to assess their competence as lead partners before climbing with them.
My question is, what is a good way to do this? I've read this question (Vetting belayers at the gym?), but I'm specifically asking about lead belay and it is obviously more complicated and the potential for a serious accident is greater. I could make sure that they have their lead card and climb easy routes at first that I'd be very unlikely to fall on, but I wouldn't be able to see their belay technique since I'd be looking at the wall most of the time.
I know that some people only let others who they know belay them, but presumably you didn't know them at first, so this only seems like a realistic option for experienced climbers who already have several lead climbing partners. I'm asking about how to find competent climbing partners in the first place.
How do you handle this situation? If it matters, I plan on only leading indoors for a while until I gain more experience.