Principles and Rules

Some weeks ago I gave a talk at My talk was about a weird experimental Kanban board, and the Leitmotiv I used was around the differences between Principles and Rules. The topic was: we often learn methodologies mocking rules (often, without getting the point) rather than trying to understand the principles behind them. This bad habit sometimes leads us to take really dumb decisions.

Well, if only I had seen then what I saw today, I would have used in my talk, since I think it would have been the perfect example.

See what I found in a recent production code.
Right now, it hangs on the wall of our open space, for all the developers to see.

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Unit tests lie: that’s why I love them

When a unit test for a method implementing some feature is green, it does not mean the feature is working. The corresponding end-to-end or integration tests reveal if it’s working or if it’s broken. To Product Owner’s point of view, end-to-end tests are all that matters. Unit tests are useless.

Unit tests are meant to lie. They rely on the often wrong assumption that the rest of the world is correctly working, but only because they are explicitly mocking it: using a fake world is a deliberate lie.

To me, that’s exactly why they are so useful.

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