One of the best interviews I've had involved coming in and just sitting with the lead dev and we then spent an hour grabbing a fairly low hanging bug that was i

One of the best interviews I've had involved coming in and just sitting with the lead dev and we then spent an hour grabbing a fairly low hanging bug that was in their system and he just had me drive and allowed me to ask questions about the folder structure or conventions they used. He could see I understood how software worked, could reason about their style and approach, and I could fix the issue. I learned about their style and approach and got at least a feel for if their code base was going to be a nightmare or not. With that said... it's hard to time your hiring interviews with when you have outstanding bug tickets that you can time box to an hour or two and don't require so much esoteric implementation details that it's a waste of time. Koans are GREAT but they do fall short on being a piece of the project that the applicant will be working on, so you miss out on seeing how the applicant reacts to your codebase and he misses out on sticking his toe in it.