Ask HN: How do you tell if developer candidates can Get Things Done?

We can use tests to tell if the person is Smart and knowledgeable. Interviews, resumes, and references all give some info, but it's still very hard to tell if a person knows how to buckle down and deliver. I want to avoid hiring the smart, knowledgeable flakes.

The latest fad is hiring them for a trial project, but the management overhead and cost is just too much. And management does not want me to expose our SCC.

If the candidate has open-source to show, great, but most don't and I don't have the luxury of choosing only the ones who do.

Has anyone tried assigning a the development of a small app as a test (i.e., not meant for your own codebase), and then outsourcing the supervision of the process? Any other ideas?