Week 07, 2026

Random Thoughts

Tests Belong to the Developer Who Wrote the Code

This week I took over a unit test from a colleague. The component was well-documented, clear design decisions, good rationale for the chosen architecture. A solid foundation to work from.

What surprised me: despite the quality of the documentation, writing the test still required more effort than expected. And reflecting on why led to a useful insight.

Documentation captures what was decided. What it can’t fully transfer is the tacit knowledge behind it: which edge cases the developer was genuinely worried about, where the subtle behaviour lives, what constraints felt natural because of how the problem was worked through. That understanding is built during development. It doesn’t end up in a spec, it stays with the person who was there.

The most natural way to preserve it is to write the tests yourself, ideally test-first. TDD isn’t just a quality practice, it’s a thinking tool. You can’t write a meaningful test before the code without deeply internalising what the code is supposed to do. The test becomes a record of that understanding.

Handing off that step means handing off a piece of the problem-solving process. Keeping it means the developer stays in contact with the problem longer, and the tests reflect that.

A small friction point this week, but a good reminder of why ownership and test-driven thinking belong together.