My Most Useful Technical Interview Question

One interview question that I’ve been using for about ten years seems to filter out more candidates than any other. It’s not a trick, and I still don’t understand how come it catches so many people. Sometimes I worry that there is something wrong with what I’m asking.

The question is this – using a text editor and not an IDE, write a simple method to take an integer as an argument and return the factorial. I make sure to explain what a factorial is and wait.

The people I’m interviewing are rarely novices. I’ve asked this from people with years of banking experience. Some of them had exciting CVs, with successful projects and all the skills I was looking for; they could talk fluently about complex technology. Yet they did not seem that familiar with code. I’ve senior developers struggle with writing a simple loop.

I ask a lot of other things in interviews. I try to be open-minded, searching for strengths rather than weaknesses. I don’t bother with tricky algorithm questions that people rehearse for interviews and forget once they get an offer. With everything else I ask, if a candidate doesn’t know the initial answer, I follow-up to find what they do know.

But I expect anyone going for a technical position to be comfortable writing a simple piece of code, to be familiar with what code looks like. Can you write a loop and check it? I try to account for the fact that the candidate might feel nervous, and might find the lack of an IDE challenging. Sometimes, I tell them not to worry too much about syntax, to use pseudocode if they like.

I’ve been interviewing developers for years, and that question is essential. The piece of code I ask for is trivial. I’ve heard of interviewers getting the same results with FizzBuzz. The example that I use is listed across the web as an interview cliche, something a prepared candidate would expect. A good candidate disposes of this quickly and moves to the next question; but some people struggle. The question shouldn’t work, but it does.

Some things learned in 20 Years of Software Development

I’ve now been a software developer for over 20 years. I started out thinking this would be a temporary diversion, but it’s grown to be something I love. I’ve been lucky enough have a wide experience of the industry, from mobile to microservices, and from three-person companies to multi-nationals. So, I decided to compress some of what I’ve learned into some short points:

  1. If a bug isn’t getting fixed this month, then you might as well not track it as you’ll never touch it. (or, to put it more positively – use a zero-bug strategy!)
  2. TDD is never going to take off. Everyone has automated tests, which is great, but I’ve never worked anywhere that used the proper TDD cycle in practise.
  3. Good project management is more important than methodology. Projects are just as messed up under agile as they were under waterfall, but we now have more meetings.
  4. The DRY principle is overrated. Too many people go for this ease of change rather than ease of reading. This is especially problematic in test code, which is mostly write-only.
  5. Focus on the data – I’ve always considered any computer system as a data-store with some code attached, and this works pretty well. If you get the transactions right, everything else will follow.
  6. The best code is simple. If it can’t be followed by junior colleagues, it’s too complicated.
  7. Projects rarely fail for technical reasons. Unless you’re doing something cutting-edge, the failure is due to something within your control. Software development is one of the least important parts of being a developer.
  8. Performance testing is hard.
  9. New technologies get less exciting as you compare them to things you already know. Like, gRPC is just fancy SOAP.