Chapter 23: fixtures, evidence in a jar

When something goes wrong in a running game, the moment passes. Link walks on, the bot re-plans, and an hour later all anyone has is a memory of "he just stood there". This folder keeps the moment. A fixture is what a running window said about itself at the time something went wrong, saved as it came out of the tool that produced it, so that the defect can be argued about with the real thing in front of you.

A fixture here is evidence, not a test input. Nothing in the build reads these files; a person does. When a fixture leads to a test, the test lives beside the code it tests and rebuilds the situation in that crate's own terms, citing the fixture in its doc comment. That way a fixture can be deleted without breaking anything, and a test never ends up testing a JSON parser.

Aside: the one that is here. On 2026-09-20 the window stood motionless in overworld area 43 for four minutes, with the player-control flag on the whole time. The decision record shows Jev choosing the right direction, over and over. The defect was underneath: the empty button press that followed each choice counted as "Link is not moving", so every plan was thrown away one decision after it was made. It is kept because it is a perfect example of a bug that looks like the model's fault and is not.

Try it. jq '.' research/fixtures/live-stall-area43.json | head -40 and see what a decision record from the old Rust brain looked like.

For the people who maintain it

In this folder

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