Test Coverage Improver

Use this skill when you need a prioritized, risk-aware plan to improve tests from coverage results.

Usage assumptions

• Focus scope is either changed lines/files, a module, or the whole repository.
• Coverage artifact must be generated or provided in a supported format.
• If required context is missing, call out assumptions explicitly before proposing work.

Workflow

1. Define scope and baseline

   • Confirm target language, framework, and branch.
   • Confirm whether the scope is changed files only or full-repo.

2. Produce coverage snapshot

   • Rust: cargo llvm-cov (or cargo tarpaulin) with existing repo config.
   • JavaScript/TypeScript: npm test -- --coverage and read coverage/coverage-final.json.
   • Python: pytest --cov=<pkg> --cov-report=json and read coverage.json.
   • Collect total, per-file, and changed-line coverage.

3. Rank highest-risk gaps

   • Prioritize changed code, branch coverage gaps, and low-confidence boundaries.
   • Apply the risk rubric in coverage-prioritization.md.
   • Keep shortlist to 5–8 gaps.
   • For each gap, capture: file, lines, uncovered branches, and estimated risk score.

4. Propose high-impact tests

   • For each shortlisted gap, output:
     • Intent and expected behavior.
     • Normal, edge, and failure scenarios.
     • Assertions and side effects to verify.
     • Setup needs (fixtures, mocks, integration dependencies).
     • Estimated effort (S/M/L).

5. Close with validation plan

   • State which gaps remain after proposals.
   • Provide concrete verification command and acceptance threshold.
   • List assumptions or blockers (environment, fixtures, flaky dependencies).

Output template

Coverage Snapshot

• total / branch coverage
• changed-file coverage
• top missing regions by size

Top Gaps (ranked)

• path:line-range | risk score | why critical

Test Proposals

• path:line-range
  • Test name
  • scenarios
  • assertions
  • effort

Validation Plan

• command
• pass criteria
• remaining risk