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The Five Underplayed Premises Of TDD

August 8, 2025

Today I got reminded of a great video of GeePaw Hill about the “Five Underplayed Premises Of TDD” .

1. The money premise:

When writing tests, we don’t do it for the art of it or other moral reasons. We do TDD because it lets us build more features faster.

2. The judgement premise:

There’s no one-size-fits all approach to building quality software. Developers applying TDD use human judgement while building software systems.

3. The chain premise:

We prefer testing very tiny subsystems that make up our larger system. Why? Because small tests are not only easier to read, comprehend and write, but also execute a lot faster compared to large-scale end-to-end tests. This is a preference, not a hard rule.

4. The correlation premise:

The internal quality of the code for a system is directly correlated to the productivity of the developers working in this code base. They go up together, and they go down together.

5. The driving premise:

Tests and testability help drive the design of a system. A code base that is highly testable, exposes certain characteristics that are generally considered as good design. People new to TDD often resist the idea of changing their design to facilitate tests. However, this is inevitable when doing TDD. It drives the design.

These 5 premises are at the foundation of every step a developer makes when using TDD. Check out GeePaw’s video if you want to learn more. The best 10 minutes you’ll probably spend this week. I promise 😄

If you and your team want to learn more about how to write maintainable unit tests and get the most out of TDD practices, make sure to have look at our trainings and workshops or check out the books section. Feel free to reach out at infonull@nullprincipal-itnull.be.

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Jan Van Ryswyck

Thank you for visiting my blog. I’m a professional software developer since Y2K. A blogger since Y2K+5. Provider of training and coaching in XP practices. Curator of the Awesome Talks list. Past organizer of the European Virtual ALT.NET meetings. Thinking and learning about all kinds of technologies since forever.

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The opinions expressed on this blog are my own personal opinions. These do NOT represent anyone else’s view on the world in any way whatsoever.

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Thank you for visiting my website. I’m a professional software developer since Y2K. A blogger since Y2K+5. Author of Writing Maintainable Unit Tests. Provider of training and coaching in XP practices. Curator of the Awesome Talks list. Thinking and learning about all kinds of technologies since forever.

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