How to choose the Mutation-CRAP limit (0.22.2) #43

2026-10-04T17:01:54+02:00

mi commented

2026-10-04 17:01:54 +02:00

The Problem

The README says that no threshold is proven, but not what a project should consider when it chooses one.
Two reasons to raise the limit came up: a Kotlin project set 16 instead of 10 for the branches the compiler adds, and the idea to raise it where only coding agents change the code.
Both look alike, but have opposite effects on what the gate demands.

The Solution

A README section "Choosing a Limit": start a ratchet at today's highest value; a higher limit also lowers the mutation score demanded from complex methods, shown for complexity 10.
Kotlin's generated branches are a reason to raise it, a measurement effect; code that nobody reads anymore is none, as the tests are then the only check left.
Version 0.22.2; no change to the plugins.

Additional Changes

The usage example in the README applies the plugin 0.22.0.

Prerequisite PRs

PR#42: this branch builds on it for the versions 0.22.1 and 0.22.2.

🤖 Generated with Claude Code

## The Problem The README says that no threshold is proven, but not what a project should consider when it chooses one. Two reasons to raise the limit came up: a Kotlin project set 16 instead of 10 for the branches the compiler adds, and the idea to raise it where only coding agents change the code. Both look alike, but have opposite effects on what the gate demands. ## The Solution - A README section "Choosing a Limit": start a ratchet at today's highest value; a higher limit also lowers the mutation score demanded from complex methods, shown for complexity 10. - Kotlin's generated branches are a reason to raise it, a measurement effect; code that nobody reads anymore is none, as the tests are then the only check left. - Version 0.22.2; no change to the plugins. ## Additional Changes - The usage example in the README applies the plugin 0.22.0. ## Prerequisite PRs - [PR#42](2026-10-04-PR%2342-plugin-0.22.0.md): this branch builds on it for the versions 0.22.1 and 0.22.2. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

mi added 1 commit 2026-10-04 17:05:46 +02:00

How to choose the Mutation-CRAP limit (0.22.2)

werkator build succeeded after 01:40

Details

57ce56828c

A higher limit also allows weaker tests; Kotlin's generated branches
justify raising it, code changed by coding agents only does not.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

mi force-pushed mihoe/choosing-a-limit from 2a8f92004a to 57ce56828c

2026-10-04 17:05:46 +02:00

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mi merged commit e7117eba20 into main

2026-10-04 21:38:36 +02:00

mi deleted branch mihoe/choosing-a-limit

2026-10-04 21:38:36 +02:00

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Reference: mi/werkcrappit#43