Layer Testing Skill

Orchestrate comprehensive layer testing with coverage analysis and isolated worktrees.

<context> Coverage-first analysis prevents wasted effort—existing tests may already cover the code you're about to test. Running coverage before writing tests reveals exactly where gaps exist, letting you focus effort on uncovered paths rather than duplicating existing coverage.

Isolated worktrees keep testing work separate from your working branch, preventing accidental commits to main development branches and enabling parallel testing of multiple layers. </context>

<constraints> - Write tests only—never modify production code during testing - Stay within the specified layer—do not test adjacent layers - Use worktree for all changes—keep working branch clean - Follow the testing strategy—do not add tests for explicitly skipped patterns </constraints> <workflow>

1. Get Parameters

From command invocation:

Testing Request:
- Module: auth
- Layer: infrastructure
- Playbook: docs/playbook.md (optional)
- Coverage Target: 100% (optional)

From natural invocation: Ask user for module, layer, playbook path (optional), coverage target (optional).

2. Get Testing Strategy

If playbook provided:

Read(${PLAYBOOK_PATH})

If no playbook: Ask user to choose:

<strategy_options>

1. Hexagonal Architecture - Domain/Application 100%, skip infra schemas
2. Clean Architecture - Use cases/Entities 100%, skip frameworks
3. Layered - Services/Logic 100%, skip DTOs/configs
4. Custom - I'll answer questions about what to test </strategy_options>

If user picks 1-3: Use template from

skills/layer-testing/templates/

If user picks 4: Ask:

• Coverage target? (100%/80%/70%)
• What to test? (business logic only / all code)
• What to skip? (types, schemas, mocks, configs)
• Build strategy from answers

Store strategy for agent use.

3. Run Coverage First

Check for existing tests:

find src/modules/${MODULE}/${LAYER} -name "*.test.*" -o -path "*/__tests__/*"

If NO tests: Skip to step 4

If tests exist:

Detect framework and run coverage (run these checks in parallel):

if [[ -f "vitest.config.ts" ]] || grep -q "vitest" package.json; then
  pnpm test src/modules/${MODULE}/${LAYER} --coverage --reporter=json-summary
elif [[ -f "jest.config.js" ]] || grep -q "jest" package.json; then
  pnpm test -- src/modules/${MODULE}/${LAYER} --coverage --coverageReporters=json-summary
fi

Parse

coverage/coverage-summary.json

:

TOTAL_COV=$(jq '.total.lines.pct' coverage/coverage-summary.json)

If 100% coverage:

✅ Already at 100% coverage!

Options:
1. Exit (nothing to do)
2. Verify test quality
3. Enhance tests

Choose (1-3):

If user picks 1, exit successfully.

If < 100%: Continue to Step 4

4. Analyze Files

Find all files:

find src/modules/${MODULE}/${LAYER} -name "*.ts" ! -name "*.test.*" ! -path "*/__tests__/*"

Categorize using strategy:

• Testable (matches "what to test" patterns)
• Skip (matches "what to skip" patterns)

Cross-reference with coverage (if available):

• Fully covered (100%)
• Partially covered (<100%, extract uncovered lines)
• Not tested (0% or not in coverage)

5. Present Analysis & Ask User

Show results:

📊 ${MODULE}/${LAYER}

Coverage: ${TOTAL_COV}% (target: ${TARGET}%)
Gap: ${GAP}%

✅ Fully Covered:
  - File1.ts (100%)

⚠️ Partially Covered:
  - File2.ts (45%, lines 10-20, 30-40 uncovered)

❌ Not Tested:
  - File3.ts (0%)

⊘ Skip:
  - schema.ts (per strategy)

Which files to test?
1. All gaps
2. Untested only
3. Partial only
4. Custom selection

Wait for user response.

6. Create Worktree

BRANCH="test/${MODULE}-${LAYER}-coverage"
git worktree add ../worktree-${BRANCH} -b ${BRANCH}

7. Spawn Testing Agent

Task({
  subagent_type: 'general-purpose',
  description: 'Test ${MODULE}/${LAYER}',
  prompt: `
Test the ${LAYER} layer of ${MODULE} module.

Strategy: Read ${PLAYBOOK_PATH}
Files: ${SELECTED_FILES}
Target: ${COVERAGE_TARGET}%
Working directory: ${WORKTREE_PATH}

Follow strategy principles.
Write comprehensive tests.
Never modify production code.
Create single commit when done.

Report:
- Coverage achieved
- Tests created
- Any issues
`
})

Wait for agent completion.

8. Verify Results

<verification> Run quality gates before completing:

# 1. Tests pass
pnpm test ${FILES}

# 2. Coverage meets target
pnpm test ${FILES} --coverage
# Parse and verify >= target

# 3. No production code changes
git diff --name-only | grep -v test | wc -l  # Should be 0

# 4. Type check passes
pnpm typecheck

# 5. Lint passes
pnpm lint

All five gates must pass before proceeding to report. </verification>

9. Report

✅ Testing Complete: ${MODULE}/${LAYER}

Coverage: ${BEFORE}% → ${AFTER}% (+${DELTA}%)
Tests: ${COUNT} new tests
Files: ${FILES_TESTED}
Commit: ${COMMIT_HASH}

Quality Gates:
✅ All tests passing
✅ Coverage target met
✅ No production changes
✅ Type check passing
✅ Lint passing

Next steps:
- Review tests in worktree
- Merge: git rebase ${BRANCH}
- Or: Continue testing other layers

</workflow>