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Change risk per class from Mutation-CRAP, cohesion and coupling (0.22.0) #41

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mi merged 1 commits from mihoe/change-risk into main 2026-10-04 16:51:32 +02:00
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mi commented 2026-10-04 16:17:06 +02:00
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Related Links

  • ADR 0008, the formula and its alternatives
  • RFC 0002, which brought LCOM4 and Ce

The Problem

The report has three values per class or method, but none says where a change most likely breaks something unnoticed.
Mutation-CRAP per method misses a large class whose many simple methods are weakly tested.
In werkcrappit, ClassReferences has no method above 6.8, but 43 % of its mutants survive.

Non-Goals

  • A limit for the change risk: the gate keeps judging the single values (@MC-CR-005).
  • Any change of Mutation-CRAP, LCOM4 or Ce.

The Scenarios

The scenarios were agreed one by one on 2026-10-04, in the new feature file 09-change-risk.feature and in 07-codecharta.feature.
Name, formula and constants were decided before: "Change risk", Mutation-CRAP over the whole class as the base (option C of three), fixed k_L = 2 and k_C = 20, a band from 30 to 100.

  • @MC-CR-001 change risk is Mutation-CRAP over the whole class: 20 methods of complexity 1 with half their mutants killed give 70, though no method exceeds 2.
  • @MC-CR-002 LCOM4 and Ce raise it, × (1 + (LCOM4 − 1)/2) × (1 + Ce/20), as an exact fraction.
  • @MC-CR-003 only scored methods count, nested classes belong to their top-level class; no scored method, no change risk; no LCOM4 counts as 1.
  • @MC-CR-004 an INCONCLUSIVE method or one without complexity voids the change risk of its class, with the reason method-not-scored:….
  • @MC-CR-005 the gate does not judge the change risk, and the methods' Mutation-CRAP stays as it was.
  • @MC-CR-006 mutation-crap.md lists the ten classes with the highest change risk, with what makes them risky.
  • @MC-CC-035 the city has the metric change_risk, a fourth scenario change-risk.ccscenario and a link coloured by it.
Verified by

The Solution

  • ChangeRisk in the metric core computes the value as a reduced fraction from the summed complexity and mutants, LCOM4 and Ce; its base is MutationCrap.of.
  • ChangeRisks joins the methods to their top-level classes; ClassDesign carries the result as ClassRisk.
    ReportData does the join, so JSON, Markdown and console read the same values, and the listener's coupling stays at its ratchet of 21.
  • mutation-crap.json has schema version 3; the gate and the export read version 3.
  • mutation-crap.md has a section "Change Risk"; the city a metric change_risk, a scenario and a link, yellow from 30 and red from 100.
  • Version 0.22.0.

Additional Changes

  • FeatureFilesTest now also checks the IDs MC-CK-… and MC-CR-… against the acceptance map; it knew only MC-… and MC-CC-….
  • The acceptance map is column-aligned, and its note on test locations moved below the table, where it no longer splits it.

Follow-up PRs

  • werkcrappit-pit uses the Gradle plugin 0.22.0: until then the nightly mutation build fails, as its gate reads schema version 2.

🤖 Generated with Claude Code

## Related Links - [ADR 0008](../adr/0008-change-risk.md), the formula and its alternatives - [RFC 0002](../rfcs/0002-cohesion-and-coupling.md), which brought LCOM4 and Ce ## The Problem The report has three values per class or method, but none says where a change most likely breaks something unnoticed. Mutation-CRAP per method misses a large class whose many simple methods are weakly tested. In werkcrappit, `ClassReferences` has no method above 6.8, but 43 % of its mutants survive. ## Non-Goals - A limit for the change risk: the gate keeps judging the single values (`@MC-CR-005`). - Any change of Mutation-CRAP, LCOM4 or Ce. ## The Scenarios The scenarios were agreed one by one on 2026-10-04, in the new feature file `09-change-risk.feature` and in `07-codecharta.feature`. Name, formula and constants were decided before: "Change risk", Mutation-CRAP over the whole class as the base (option C of three), fixed `k_L = 2` and `k_C = 20`, a band from 30 to 100. - `@MC-CR-001` change risk is Mutation-CRAP over the whole class: 20 methods of complexity 1 with half their mutants killed give 70, though no method exceeds 2. - `@MC-CR-002` LCOM4 and Ce raise it, `× (1 + (LCOM4 − 1)/2) × (1 + Ce/20)`, as an exact fraction. - `@MC-CR-003` only scored methods count, nested classes belong to their top-level class; no scored method, no change risk; no LCOM4 counts as 1. - `@MC-CR-004` an `INCONCLUSIVE` method or one without complexity voids the change risk of its class, with the reason `method-not-scored:…`. - `@MC-CR-005` the gate does not judge the change risk, and the methods' Mutation-CRAP stays as it was. - `@MC-CR-006` `mutation-crap.md` lists the ten classes with the highest change risk, with what makes them risky. - `@MC-CC-035` the city has the metric `change_risk`, a fourth scenario `change-risk.ccscenario` and a link coloured by it. ##### Verified by - [ChangeRiskTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/core/ChangeRiskTest.java) - [ChangeRisksTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/design/ChangeRisksTest.java) - [JsonReportTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/report/JsonReportTest.java) `theClassEntryCarriesTheChangeRisk` - [MarkdownReportTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/report/MarkdownReportTest.java) `theTenClassesWithTheHighestChangeRisk` - [GateTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/gate/GateTest.java) `changeRiskIsNotJudged` - [ReportInputTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/codecharta/ReportInputTest.java) `theChangeRiskOfTheReportIsReadBackExactly` - [CodeCityTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/codecharta/CodeCityTest.java) `theCityShowsTheChangeRisk`, [CodeCityScenariosTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/codecharta/CodeCityScenariosTest.java) `changeRiskIsTheFourthScenario`, [CodeCityPageTest](../../werkcrappit-pit/src/test/java/de/javagil/werkcrappit/pit/codecharta/CodeCityPageTest.java) `thePageOpensTheCityByChangeRisk` - [CodeChartaFunctionalTest](../../werkcrappit-gradle-plugin/src/functionalTest/java/de/javagil/werkcrappit/gradle/CodeChartaFunctionalTest.java) `aRealBuildWritesAValidCity` ## The Solution - `ChangeRisk` in the metric core computes the value as a reduced fraction from the summed complexity and mutants, LCOM4 and Ce; its base is `MutationCrap.of`. - `ChangeRisks` joins the methods to their top-level classes; `ClassDesign` carries the result as `ClassRisk`. `ReportData` does the join, so JSON, Markdown and console read the same values, and the listener's coupling stays at its ratchet of 21. - `mutation-crap.json` has schema version 3; the gate and the export read version 3. - `mutation-crap.md` has a section "Change Risk"; the city a metric `change_risk`, a scenario and a link, yellow from 30 and red from 100. - Version 0.22.0. ## Additional Changes - `FeatureFilesTest` now also checks the IDs `MC-CK-…` and `MC-CR-…` against the acceptance map; it knew only `MC-…` and `MC-CC-…`. - The acceptance map is column-aligned, and its note on test locations moved below the table, where it no longer splits it. ## Follow-up PRs - werkcrappit-pit uses the Gradle plugin 0.22.0: until then the nightly mutation build fails, as its gate reads schema version 2. 🤖 Generated with [Claude Code](https://claude.com/claude-code)
mi added 1 commit 2026-10-04 16:17:06 +02:00
Change risk per class from Mutation-CRAP, cohesion and coupling (0.22.0)
werkator build succeeded after 04:33
Details
87ef798de2 
Mutation-CRAP over all scored methods of a top-level class, times
(1 + (LCOM4 - 1)/2) and (1 + Ce/20), as an exact fraction (ADR 0008).
Report schema version 3, a Markdown section, and a fourth view in the
code city. The gate does not judge it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
mi merged commit 18248cb975 into main 2026-10-04 16:51:32 +02:00
mi deleted branch mihoe/change-risk 2026-10-04 16:51:32 +02:00
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Reference: mi/werkcrappit#41