Ask HN: validating that the cofounder is the right one

I'm starting to work with a friend from High School on a business. We haven't seen each other in 7+ years at this point, and weren't best friends back then. I've learned my lesson the not so hard way not to accept just anyone as a cofounder. Since neither of us have any background that can really be said to be 100% verifiable, how should I approach like a bailout, or trial period? I'm technical, and we're building software, he's financial, marketing, business, and grapic design. I'll be building the product myself. I realize the other stuff is as important, but how can I? should I? validate that he's going to cut it.

I myself feel I can be validated by having something to show after a few weeks to a month of work.