This would be a fascinating, probably more reliable way to test someone: ask them to explain in as much detail as possible what a code sample did - what problem

This would be a fascinating, probably more reliable way to test someone: ask them to explain in as much detail as possible what a code sample did - what problem it appeared to be solving, and what edge cases it attempted to handle as well as perhaps some it would have failed to handle. If you provide them a good sample, the function names and behaviors should give a really good sense of direction to the candidate, and the harder questions would be answered by the details of the code.