TDD Pairing – What I Missed

Since this is a training exercise, and I am working with a senior developer who is a good teacher, we spent some time reviewing our first pairing session. To teach me while we paired, the developer had created a situation to see if I could spot a problem. I of course missed it. During our TDD session, my primary focus was on thinking of testing ideas. The developer however was simultaneously thinking of making the code testable, improving the software design, and continuously improving the testability of the code. These three activities he says are the hallmarks of a good design.

Leading me down the garden path in the hopes of teaching me something, he deliberately developed a bad code smell and tried to guide me into seeing it. I was so focussed on generating testing ideas that I missed it. He deliberately made the unit tests awkward and difficult to implement. I trusted his design and took that for granted as a technical issue that I didn’t understand. I didn’t realize that the fact that the tests were onerous and difficult to set up and code was a bad test smell.

The lesson that I learned is that if we can add tests simply, it’s a sign of a good code design. Since the tests were awkward and I was completely dependent on the developer to add them, I needed to be concerned. As a tester, part of my job when pairing in a test-driven development situation is to watch for bad testing smells. Those bad smells in the tests are symptoms that something is wrong with the code. The developer pointed out that when it’s hard to test, it’s time to improve the code. When testability is improved, a byproduct is a better design.

At the end of the day, I was thinking about more test ideas and felt we needed to add much more to the existing design. The developer however realized we were in trouble and needed to refactor the existing code to make it more testable. Lesson learned – I need to watch that we can add tests easily. That is a sign of a good design. It doesn’t take a lot of programming skill to realize that some unit tests are awkward while others are simple and elegant. I’m also fairly confident that testers who don’t program would be able to learn to see the difference quite quickly after spending time with a developer who can demonstrate good and poor unit tests.