return to blog listing Reading time 9 min

TDD & Pair Programming in practice

Luka Sekovanić Developer
Published on:
Share this article!

When I was a Java software engineer with a few months of experience I encountered TDD only through participating in a few workshops or from books & blogs. I thought “yeah, yeah, it is all nice in theory, but who really uses TDD in practice”? C’mon, really? 

Just do a story or a task as fast and as good as you can, maybe write some integration or unit tests, maybe leave it “for later” … meh… who really cares… It’s a legacy project so we don’t want to put too much effort into it and hopefully we’ll rewrite it soon into a better technology and/or framework. What about Pair programming? LOL. No way am I going to work with some random dude all the time. What if the person annoys me or they will not want to do anything, or even worse, what if they are so much better and faster that they will not want to explain anything and I will not get the chance to learn? Also, who has the responsibility for the story in pair programming?

All these were my prejudice & questions about the aforementioned concepts. In this blog, I’m going to tell you how working on a Belgian public sector project has given me an opportunity to work in pair & made me disciplined about writing tests before the implementation.


TDD (Test Driven Development) is, simply put, a way of developing where we first write a test and the implementation comes afterwards. To avoid repeating or copying definitions, I’ve provided some useful links for you to check out, and the rest you can find easily on the Internet.

Here you can watch what Uncle Bob has to say about it:

If you wish to practice TDD, there are some cool examples on the web like this:

Also, it’s always nice to read a book:

Pair programming

Pair programming is, in short, two people developing at the same time. This means that one developer types the code while the other one gives suggestions and warns about possible bugs in the code. Usually they switch in code writing and assisting. Sometimes one writes a test and the other one writes the implementation or one writes code for the first half of a working day and the other one writes for the second half of the day. It all depends on how two people like to work, but the idea is that both members of the pair are focused on the work at the same time in order to produce quality and bug-free code.

You can read more about pair programming here:

How does it look in practice?

Way back, when I had only a few months of experience as a Java web developer, I didn’t even know there was a different way of programming than: “do the implementation and after that make sure it works by writing tests for it”. The first time I heard about TDD was during a Spring framework introduction workshop I attended, but I wasn’t familiar with pair programming until I started working at my current company There I’ve been told that such an approach leads to better code quality & a smaller number of bugs in the code. Ok. I understood that TDD is in theory the “right” way to develop code, but I was skeptical at first if people really develop in a TDD way and how pair programming even works or helps.

My first real experience with TDD and pair programming happened while working on a big project with around 1M 890k lines of code (1M 007k were the test code). We are also talking about the project that had its first commit in 2010 after 2 failed developing attempts that hadn’t followed the concepts mentioned earlier. So how do you work on that kind of project and keep it maintainable for all these years?

Some of the most important ways to help keep the code base maintainable is not only using TDD & pair programming, but also developing according to clean code and DDD (Domain Driven Design) principles. All this pays off in the long run, especially when you have complicated domain and business logic in the project.

Alongside things mentioned above, we also have a strict development process that we follow:

  • Daily standups – say what you did yesterday, what are you doing today & is something blocking you
  • Pair modeling – a process of creating a document that two people wrote with functional & technical summary of a story that needs to be implemented
  • Story kickoff – after the pair modeling, a story is divided into tasks and presented to the team. The team asks questions and also gives suggestions if something can be done better
  • Pair programming – two developers actively develop a story, one takes a lead on the story which means he/she will work on it until it’s done, and the other member of the pair changes on the daily basis
  • TDD – we strongly try to keep the discipline of writing tests first. Unit tests usually go first and the implementation afterwards. Production code is also backed up with integration and end-to-end tests
  • DDD – while developing, we should be aware that the project must follow DDD concepts and rules
  • Proxy check – check the story with proxies (proxies are people who talk to users and make sure that stories they wrote are functionally OK)
  • Merge/pull requests – create a merge request so that other developers can take a look at your code and approve the code or request changes if necessary

Yeah, yeah, it is all nice in theory, but in practice who really uses TDD?

We do. After a story kickoff you sit with your other half of the pair for that day and you start working on the story. First you create a test, then implementation, then some more tests and so on. Of course, do not forget to refactor! Alongside unit tests, often you need to add integration tests and/or end-to-end Selenium tests to check if everything is ok when user works with the web application on a browser.

No way am I going to work with some random dude all the time!

IMHO, working with people is sometimes the hardest part of my job, but also, working in pair has more benefits than disadvantages. Yeah, it can happen that you aren’t so fond of the person who is pairing with you that day, but that happens rarely and you switch pairs every day. Sometimes discussions can take a lot of time, but in the end, they also teach you how to defend and explain why you do what you do & to develop communication “soft” skills. Also, I learned a lot about how other people think & work. With pair programming you get a chance to share knowledge a lot, because you are literally working next to another developer on the same thing. In the end you do not escape responsibility. You do share it with your pairs, but if you are the story lead, then you should ensure that it is implemented as best as possible in the code and functionally.

TDD & pair programming often work as shown in this simplified scenario:

Developer A: Oh, this story is easy like we talked on the kickoff! Let’s add a method to the service to search for files that have status “ACTIVE”.

Developer B: Great, we are working according to TDD so let’s start with a unit test! We should add a test that creates two mock files. First one should have “INACTIVE” status and the other file should have “ACTIVE” status. This test will then call our method and assert that it returns a list with only one “ACTIVE” file.

Developer A: Nice, I’ll do the test and you can do the implementation and after that we switch?

Developer B: It’s a deal. I’ll help you by watching and commenting and I expect from you the same when I’ll be writing code.

Hopefully our two developers created some quality code with good test coverage. But even if they didn’t, they still have to pass the proxy check and merge request reviews. 


After working for more than a year according to TDD and in pair, some of my opinions on those subjects have changed:

  • TDD changes the way you think and work. The ability to create a test before the implementation proves that you understand what needs to be done. With each test you improve and refactor your code, and tests ensure that the code does what it was intended for.
  • If you are working on a big project, it is hard to know everything and working in pair speeds up the development.
  • Two people usually do the discussions and explanations out loud and that maybe wouldn’t happen so often with “solo” development. This leads to better knowledge sharing, code quality and edge case test coverage.
  • I met some amazing people and each of them has their own unique way of thinking. I learned a lot from them – sometimes it was the use of some new IDE shortcuts, sometimes it was how to think in DDD way and sometimes we learned together about the project and technologies like Java language, Spring framework or Hibernate.
  • I’ve found my preferred way of how to pair program and, in my experience, I remain most focused if I switch roles based on test/implementation cycle.

I hope that this blog has given you some idea how TDD and pair programming look in practice. If you have more questions about it, feel free to send me an email at:

Don’t forget to share this article!