Bringing a programmer in for an interview and a coding test can lead to some interesting experiences, both for the interviewer and the interviewee. Most end up with the hiring manager telling them that they'll "be in touch," but sometimes a candidate just nails it. That's when you consider extending a job offer before they get a chance to leave the building.
At TimeTrade we run a coding test during interviews that, for the majority of programmers, should take about two hours in total to complete. The whole test is comprised of a number of small problems to solve, each harder than the one before. That gives us a good initial gauge of performance based purely on completion time: if everything has been solved in under an hour, we'll be smiling. But if two hours pass and even the first problem still hasn't been solved, the candidate will most likely just be shown the door.
Above and beyond just solving test problems quickly, here are some signs that a programmer is truly awesome and should be handed a job offer before they leave your building:
1. They present multiple solutions
I recently interviewed a programmer who solved an entire set of tests twice: once with iterative solutions, and again recursively. I quickly made him an offer. Finding multiple solutions to a problem is a skill that engineers will need to use every day.
2. They write full documentation
Last year I interviewed someone who was so diligent, so detailed and so professional about his work that he created full Javadoc and comments for his code before he considered the solution complete. He even wrote fully automated unit tests and checked their coverage percentage. When I came back into the room at the two-hour mark and found him typing furiously I initially thought he was having trouble with the test, but he was actually in the process of adding HTML formatting to his Javadoc. Engineers who do this intuitively are the kind you'll want on your team.
3. They improve the test
We deliberately create tests that have some minor issues lurking within them, purely to see if the candidate (a) spots them and (b) is willing to fix them. It might be an inconsistent usage of quotation marks for strings, misleading variable names or anything along those lines. Candidates that look at all of the provided code as the test -- not just the pieces we've asked them to write -- are the ones who will do the same in our real product once they join our team.
An engineer who is willing to tell a potential employer that the supplied test contains problems shows that they consider the quality of their work to be more important than just agreeing to do what they're told. Hire them and they'll likely work wonders for your product, going above and beyond their assigned areas to make improvements where they are needed.
4. They refactor smartly
Most candidates like to get a solution working, then sit back and breathe a sigh of relief that they finished it successfully. That's good, but rarely good enough to justify an on-the-spot job offer. The candidates that solve the problem but then jump right back in to refactor it are in a different category entirely. Their choice of algorithm doesn't feel right, and they can't ignore the feeling that it could be more efficient. Their code has some duplication in it, and that burns them up inside. These are the candidates who refactor, rewrite and improve their solution until it's been crafted.
This can be a double-edged sword, though. If the candidate just keeps rewriting because they're not happy until they reach a mythical point of "perfection," there's a chance they are one of those programmers who doesn't know when to stop (and similarly, ship). However if they watch the clock carefully and are able to both solve the problem and refactor their solution before their time runs out, that's a really good sign that you should consider an offer.
5. All other signs point to "hire"
Sometimes there are plenty of non-technical signs that you've found the right candidate. Your other team members take you aside and tell you, "We have to hire this lady." Their personality feels like a great fit for the team. They have relevant and recent experience in what they'll need to do. You know some people who have worked with them before and they tell you they are wonderful to have on a team (and that they'd hire them again in a second). The candidate is excited about the company and the opportunity and is hungry to start contributing.
If the candidate passes technical muster and all other signs point to "hire," why wait? If you do, you may lose the candidate to another employer who knows how to read the same signs faster than you can. Instead, be decisive and make the offer fast, thereby telling the candidate how much the company wants them on board. It will help start the whole relationship off on the right foot, for both parties.
So the next time you've got a wonderful candidate in your building, don't assume someone even better will arrive the next day. Make them an offer and get yourself -- and the candidate -- back to work.