feat(plop): add VRT + Test unit to component scaffolding

[aramos-adobe]

Description

Adds two standalone plop generators to the 2nd-gen scaffolder and extends the existing component generator so a new component ships with VRT coverage out of the box.

• test — retrofits an existing component with unit (*.test.ts) and accessibility (*.a11y.spec.ts) test files.
• vrt — retrofits an existing component with a Chromatic VRT story (test/vrt/<name>.vrt.ts).
• component now also emits a baseline .vrt.ts stub alongside the test/a11y files it already scaffolds.

The retrofit generators are safe by design: they guard that the target component exists (aborting with a clear message otherwise), use skipIfExists so they never clobber existing files, and format only the test/ / test/vrt/ subtree they write. All generated output is lint-clean and Prettier-formatted; TODOs mark where the author fills in component-specific detail.

This is build-time authoring tooling. It adds no runtime code and changes no shipping component. Stacked on #6391 (base branch caseyisonit/gen2-plop-templates).

Motivation and context

Post-migration, the recurring authoring task shifts from creating new components to adding test and VRT coverage to the 100+ components that already exist, many migrated before the scaffolder landed. The component generator can't help there (re-running it collides with the existing files), and it previously shipped no .vrt.ts at all. These standalone generators make adding that coverage deterministic and one-command, and giving component a VRT stub means new components carry visual coverage from the start.

Related issue(s)

• SWC-2448

Screenshots (if appropriate)

N/A — build-time tooling, no runtime or visual change.

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

• component now scaffolds a VRT file

  1. From the repo root, run yarn plop component "test-widget" --force
  2. Confirm the skeleton includes 2nd-gen/packages/swc/components/test-widget/test/vrt/test-widget.vrt.ts alongside the test/*.test.ts and test/*.a11y.spec.ts files
  3. Clean up: rm -rf 2nd-gen/packages/{core,swc}/components/test-widget and git checkout -- 2nd-gen/packages/core/package.json

• test and vrt retrofit an existing component

  1. Scaffold a component (yarn plop component "test-widget" --force), then delete its test/ directory
  2. Run yarn plop test "test-widget" --force and yarn plop vrt "test-widget" --force
  3. Confirm the test/a11y files and test/vrt/test-widget.vrt.ts are recreated, and the VRT import shape matches button.vrt.ts
  4. Clean up as above

• Retrofit generators guard against a missing component

  1. Run yarn plop vrt "does-not-exist"
  2. Expect a clear abort message and no files written

• Output is lint-clean

  1. On a generated component, run yarn lint, yarn lint:css, and yarn lint:docs-pages
  2. Expect all to pass (the a11y ARIA snapshot and VRT grid are intentional TODO scaffolds)

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

Accessibility testing checklist

This PR adds build-time scaffolding tooling. It introduces no runtime UI, component, or behavior, so there is no interactive surface to test here. The accessibility of any component created from the generators is validated during that component's own migration, not in this PR. The templates intentionally seed accessible defaults (label/slot content in stories, an ARIA-snapshot a11y spec) as a starting point, each marked with TODO for the author to complete.

• Keyboard (required — document steps below)

  1. No runtime UI is added by this change; there are no keyboard interactions to verify.
  2. Confirm no regressions: the change is isolated to 2nd-gen/scaffolding/.

• Screen reader (required — document steps below)

  1. No runtime UI is added by this change; there is nothing for a screen reader to announce.
  2. The generated *.a11y.spec.ts provides an ARIA-snapshot scaffold so each component carries screen-reader coverage from the start.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 33f321e

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[github-actions]

📚 Branch Preview Links

• Storybook (Gen2, dev mode)
• Storybook (Gen2, prod mode)
• Documentation Site (Gen1)
• Storybook (Gen1)

🔍 Gen1 Visual Regression Test Results

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

Deployed to Azure Blob Storage: pr-6574

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If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.