My Technical Challenge (and how I improved the process for additional hires)

Hopefully you’ve now read the two Technical Challenge posts by Ieuan and Gareth. This post is going to explain a bit more generally about the process which they went through and how I evolved it from the assessment that Alex and I took to something that was a bit more representative of the way that we work in the lab.

This turned into quite a long post, so have some contents:

Introduction - The Original Technical Assessment

Alex and I interviewed for our roles in February 2020, as the project hadn’t got started yet, the technical interview process was run by the University’s central software development team. They feel that their process works well and reflects the style of work they often have to deal with, sometimes they have to work under a lot of pressure with someone looking over their shoulder.

The technical challenge they use is a 3hr in-person (pre-covid) coding challenge with a very open brief, they want the candidate to build something of their choosing which showcases their abilities, their creativity and ability to present and “sell” an idea. I’ll include this original brief at the bottom of the page.

My Approach

3 hours is not very long to showcase your abilities and make a good impression.

I decided to try and spin up a full-stack Ruby on Rails application and host it within the time frame. Spinning up a Rails app can be pretty quick. Rails has generators for models, migrations and controllers. I’ve also built quite a few Rails apps from scratch, but three hours was still a tough target. One of the other big challenges was working out what to build. An open scope gives plenty of room to showcase creativity, but coming up with an idea is hard. I wanted something which was a basic CRUD app with user authentication, what it actually did wasn’t too important.

The idea I came up with was called Postcards from a Stranger. The “pitch” was that new students often feel isolated and lonely. Postcards would allow them to send and receive postcards from strangers which would hopefully help alleviate some of the isolation feeling. It was a fairly basic idea, but had roots related to the University and was simple to explain and build.

I knew three hours was going to be a challenge, so the first thing I did, once I had an idea I was happy with, was build it - and keep track of the time. The first time through it took a couple of hours to figure out the overall structure, the models and everything. Total build time was around 10 hours.

10 hours wasn’t great, but there was a lot of figuring out the shape of the app in that. So I moved to a new folder and tried again. The second time took roughly half the time. Which was a lot better, but still needed to be cut down. At this point I started writing myself a crib sheet, documenting step by step all of the terminal commands and customisations I needed to make. You can see this final version of this walkthrough here.

Building with the walkthrough took the time down to about 3.5 hours, which was getting a lot closer to the target. One of the things that was taking me a lot of time still was building the HTML and CSS for the app. HTML and CSS are markup and styling, they don’t really showcase programming ability. So I decided to cheat, I could write these in advance and copy them into the new directory. That way I could spend the time in the assessment on writing the application logic in ruby and getting the infrastructure deployed.

Another round of practice, with prebuilt HTML and CSS, took the build time down to two hours. It was very rushed but it was manageable. I knew there would be quite a bit of extra time on the day explaining what I was doing and talking about design choices.

Suffice to say, everything went well on the day. You can see the code on GitHub and the live version on Heroku.

Updating the Challenge

Building something in such a short period of time, with someone sat watching over your shoulder was an interesting experience. I felt as though it definitely added additional pressure which doesn’t necessarily facilitate the best performance.

We were looking to hire two more developers and I was given the chance to improve the process. Along with tweaking the job description, I felt it would be good to update the technical portion of the process. The first thing was changing it from an “assessment” to a “challenge” with the aim of making it less intimidating.

We still wanted to get an insight into our candidates' technical capabilities but change the format to better reflect the working environment within the team. I also wanted it to be something that wasn’t a waste of candidates time.

I decided to keep the open brief of the initial challenge because I wanted candidates to build something which played on their strengths, as well as showing off a bit of their creativity, but I also gave some examples and suggestions if they were really struggling. Hopefully with this, candidates could build something which could form part of their portfolio for any future applications.

The biggest change was moving away from the short time frame, in-person assessment. I wanted to give candidates enough time to do something they would be proud of. I also wanted to ensure that they would be able to spend enough time to do the challenge justice. I settled on a Thursday evening until a Tuesday morning, this should give a full weekend and three evenings (presuming there were other work commitments).

In order to ensure fairness (and that the work was their own) I mandated the use of version control. By requiring them to use a version control system (e.g. git) we can see that they have only worked in the specified period and they are not committing large chunks of code which is not their own. At the end of the challenge, all they needed to do was send us a link to their code repo.

Following the challenge and before the formal interview, we’d have a technical debrief. In this the candidate would be allowed 15 minutes to demonstrate their project then 15-30 minutes of technical questions about their codebase to assess their competency and ensure that they understand what they have submitted. The final portion of time will be asking the candidate to make a couple of minor changes to their project to watch them work through it and get it working. 


This format allowed us to gain a strong insight into the candidates technical ability, provide an interview task closer representing the working environment of the of the lab and allow candidates to perform to the best of their ability. It seemed to work well for Gareth and Ieuan!

You can read the brief which was sent to candidates below. If you’re job seeking at the moment, why not give it a go. If you’re an employer who would like to use this format, please ask first, but I’m not going to say no! If you have any questions or thoughts on how this could be improved, or if you spot any mistakes, then please get in touch!

Original Assessment Brief

Senior Developer Assessment

You will be given 2.5 hours to develop a piece of software that showcases your ability with regards to the following criteria from the job specification:

You can choose any kind of application you want (e.g. a web site, console application, API, App, etc.) provided it enables you to easily demonstrate your competency against each of the criteria in question.

We will provide a laptop with Visual Studio 2019 installed. It is important to us that you get the best opportunity to demonstrate what you can do, so if you prefer a different development environment then please contact contact person in advance of the assessment to discuss.

You will have access to the Internet during the assessment. However, you will be required to develop the solution from scratch on the day – no prebuilt solutions downloaded from GitHub please!

Prior to the day, please prepare a 5-minute pitch for what you intend to build (no more than 5 minutes – you will be timed!). You will deliver the pitch, answer any questions that the panel might have and then dive into the coding. The pitch will be assessed so use whatever technique you
believe will be the most impactful in selling your idea.

Following the assessment, the first part of the interview will consist of technical questions about the solution you have developed and how you feel your choices demonstrate competency against each of the criteria in question.

New Challenge Brief

Congratulations on making our shortlist! We’re really excited to get to know you a bit better and see what you can do. Our interview process is going to consist of three steps, a technical challenge, a technical debrief of that challenge and then a more formal interview.  

The Technical Challenge 

Your technical challenge will start at Thursday at 16:00 and run until Tuesday at 10:00. We would like you to build a piece of software that you feel showcases your abilities and your competencies against as many of the requirements from the criteria in the job description as possible. What you build, what language you use and how you build it is entirely up to you provided it enables you to easily demonstrate your competency. 

We don’t need you to fit everything that your capable of into this one project, we’re looking for you to really show off your working process, that you can write clean code that’s easy to understand and that you try and follow best practices (such as SRP, DRY and KISS). 

Any time after the challenge starts, we want you to create an entirely new code repository (our preference would be GitHub, but if you really want to use something else then go for it). Then you can crack on with building your project. We’re keen to emphasise that we will not accept any commits outside of the challenge time frame. 

We would like you to follow git best practices and to be writing clean, well documented code. You’re more than welcome to use a framework and libraries of your choice but don’t just submit a pre-built solution. We’re looking to see the process that you go through as you build your software. We would like to see a well structured ReadMe accompanying your repository (a in the root folder is ideal). 

By the deadline on Tuesday, we want you to send us a public link to your repo, fingers away from keyboards after this time, no commits or merges after this time please!  

We appreciate that coming up with an idea to build something from scratch is not easy. If you’re struggling for inspiration then here are a few examples of what we think you could achieve during the time frame. 

The Summoner (Currently broken as infrastructure has been turned off), GitHub , Summoner Blog 

Expertise Directory, GitHub 

Postcards from a Stranger, GitHub 

 If you’re still looking for a bit more inspiration, these two blog posts have a few reasonable ideas. 

The Technical Debrief 

After we’ve had a chance to review your code, you’ll have a debrief call with a couple of our developers.  

The first part of this call will be to demonstrate your project, show us what you’ve built and talk us through your motivations behind your choices – both in what you built and how you built it. You’ll have 15 minutes to show us everything you want to. 

Following your demo, they’ll be about half an hour to field questions from our developers about your project. 

The Interview 

The interview will take place with a panel from our staff who’ll ask you a range of questions, some technical, some not. This is also your chance to ask any questions you have for us.