Phase 8: unit tests for config, AWS params, and GitHub flow

[kurok]

Part of plan #15. Phase 8 — Testing & CI.

What's already in place

• #3 — .github/workflows/pr.yml now runs on all PRs (not just to main):
  • lint-code — npm run lint.
  • verify-dist — rebuilds dist/index.js via ncc and fails if it drifts from committed bytes.
  • verify-runner-url — HEADs the pinned actions/runner release asset.

Coverage today is entirely build-side; zero unit tests.

What's missing

Real unit tests for:

1. Config parsing (src/config.js). Every action input has validation logic (mode must be start/stop; when mode=start, ec2-image-* + instance type + subnet + SG are required; etc.). None of that is tested.
2. AWS parameter generation (src/aws.js). startEc2Instance assembles a complex RunInstances request (ImageId, UserData, TagSpecifications, IamInstanceProfile, BlockDeviceMappings once Phase 6 lands). An errant change silently produces an instance that boots but can't register.
3. User-data construction. The bash script assembled in startEc2Instance is a template with interpolation; unit-testable as a string.
4. GitHub API mocks (src/gh.js). Registration-token retrieval, runner-registered polling, remove-runner flow. Mock @actions/http-client or stub at @actions/github.

Proposed stack

• Jest (already the de-facto GitHub Actions testing framework).
• aws-sdk-client-mock once Phase 1 lands (v3 mocking is natively supported). Until then, stub the v2 client.
• nock for GitHub API interactions.

Proposed structure

tests/
  config.test.js          # input parsing + validation
  aws.test.js             # RunInstances params, user-data string
  gh.test.js              # registration/removal token flows
  index.test.js           # start() / stop() orchestration

CI wiring

Extend .github/workflows/pr.yml:

  unit-tests:
    name: Unit tests
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: npm
      - run: npm ci
      - run: npm test

Add npm test script to package.json → jest.

Acceptance criteria

• Jest + supporting test deps added to package.json devDependencies.
• tests/ directory with files covering config / aws / gh / index.
• npm test runs the full suite locally in <10 s.
• unit-tests job wired into pr.yml and green on this PR and feat: bump actions/runner to v2.333.1 for node24 support #3's follow-ups.
• Coverage report produced (e.g., via jest --coverage) — no specific threshold, but the numbers are published on the PR.

[kurok]

Phase 8.a landed via PR #16 — covers utils.js + config.js.

Phase 8.b (tests for aws.js + gh.js + index.js) will be filed as a follow-up after Phases 1, 4, 5 land — testing those against their current shape means tests thrown away mid-rewrite.