Strengthen an area’s tests

Apply the common work contract within the authorized scope. It owns required implementation, verification, review and completion obligations; this skill supplies methods. Use /haechi:delegate for a bounded worker task when independent execution helps. Existing step names below are compatible delegation entry points, not an exclusive workflow state.

The main session runs these steps. Scope, delegation, authorization and completion requirements are in the session rules. Use /haechi:mutation-check for each unit and a worker with /haechi:attack-tests when separate context or independent challenge helps. Use /haechi:sweep for useful independent units. This file adds only what is specific to hardening an area. Principle files are two levels above this skill's folder (<this skill's folder>/../../principles/<name>.md): behavior-tests and sibling-paths apply.

Task focus

Establish the area's mutation results, or say "not measured" if unknown. The easy mistake is scope: "harden the tests" with no folder can mean the whole repo. Example: "src/invoices not measured; formatDate.ts has no test file."

Steps

1. Clarify the task. Establish the area's current mutation results and the intended improvement. Consider /haechi:spec using its description while establishing the scope and success criteria; preserve the tests-only boundary. Only tests change; source code stays unchanged. Show mutation results before and after per unit and passing tests. Fixed labels and tables are optional.
2. Choose units. Work directly for a tightly coupled area, or use /haechi:sweep when independent units benefit from separate context. A unit can be a source file plus its tests. Order:
   1. files under riskPaths in .haechi.json;
   2. files with many recent bug fixes (git log --oneline --grep=fix -- <file>, or the repo's commit convention for fixes);
   3. files without tests;
   4. the rest. For the cost preview, estimate mutants per file (the mutation-check limit, default 20) times the unit's test run time.
3. Harden each unit. Work directly or give a worker with /haechi:attack-tests this brief when independent challenge is useful:
   • Run mutation-check before changing anything, with a per-file limit and --lines 1-<last line of the file>. Without --lines it mutates only lines changed against HEAD, which on a committed file is nothing.
   • Judge each surviving mutant: a real gap gets a stronger assertion or a new case; an equivalent mutant (behavior cannot change) gets a one-line reason and is excluded.
   • Touch existing tests in exactly two cases: a mutant survived, or a test is tied to internals and gets rewritten against observable results. Each new test catches a different mutant or path. A file with no tests gets new behavior-based tests.
   • A real bug found: do not fix the source. Record it the repo's way (AGENTS.md; otherwise a skipped test named BUG: <expected behavior>). The user decides what happens to it.
   • Run mutation-check again after, with the same --lines as before.
4. Review each unit as it finishes. Check:
   • tests assert behavior a caller observes, not internal calls;
   • no mocks of the unit's own internals, no render snapshots;
   • time and randomness are fixed;
   • fixtures are synthetic. Then commit the completed unit.

5. Report. Give the before/after results, equivalent mutants, test changes and bugs found for each unit. An optional table:

   Unit	Survived before → after	Equivalent	Tests added / changed	Bugs found
   src/utils/formatDate.ts	4 → 1	1	2 / 1	—

Extra DONE evidence

Mutation results before and after for every unit, the equivalent mutants with their reasons, and the test run passing. No source file in the diff.

Delegation contracts

These compatible entries identify delegated methods, not an exclusive workflow or a mandatory agent sequence. Packet assembly also supplies the canonical common work contract. The main session fills the named context fields and task-specific acceptance criteria; detailed procedures and principle bodies stay in their referenced files. read-only means repository files remain unchanged; authorized temporary or report outputs must be named separately in artifactPaths.

{
  "attack": {
    "skills": [
      "attack-tests",
      "sibling-path-map",
      "mutation-check"
    ],
    "principles": [
      "sibling-paths",
      "behavior-tests"
    ],
    "checks": [],
    "writeScope": "scoped",
    "contextRequired": [
      "repository",
      "requirements",
      "changedFiles",
      "ownership"
    ],
    "completion": [
      "Demonstrate that tests detect the targeted defects without weakening expected behavior."
    ]
  },
  "review": {
    "skills": [
      "verify-work",
      "review-diff",
      "impact-map"
    ],
    "principles": [
      "evidence-levels",
      "behavior-tests"
    ],
    "checks": [
      "agent-defects",
      "sibling-paths",
      "dry",
      "yagni",
      "kiss"
    ],
    "writeScope": "read-only",
    "contextRequired": [
      "repository",
      "requirements",
      "base",
      "changedFiles",
      "priorEvidence"
    ],
    "completion": [
      "Report concrete defects with expected and observed behavior and affected consumers.",
      "Distinguish passing checks, failures, missing proof and unresolved expectations."
    ]
  }
}