fix(test-helpers): make @primer/react/test-helpers runtime-agnostic

[adierkens]

Closes #

Makes the published @primer/react/test-helpers entry runtime-agnostic so it works with both Jest and Vitest consumers.

Today the file hard-references the jest global to create mock functions for its JSDOM polyfills (ResizeObserver, HTMLDialogElement.showModal/close, HTMLCanvasElement.getContext, Element.scrollIntoView, matchMedia, CSS.escape/supports). Any downstream consumer that imports @primer/react/test-helpers from a Vitest test currently hits ReferenceError: jest is not defined. Primer itself migrated off Jest in #6452 but kept this published helper as Jest-only, so Vitest consumers couldn't use it.

Changelog

New

• Nothing added.

Changed

• packages/react/src/utils/test-helpers.tsx — replaces every bare jest.fn(...) call with a small mockFn(...) helper that detects globalThis.jest?.fn or globalThis.vi?.fn at runtime and falls back to a plain no-op function if neither is present. Mock-style introspection (expect(fn).toHaveBeenCalled(), etc.) continues to work for both Jest and Vitest consumers; consumers without a test runtime get a silent no-op which is sufficient for the polyfill use case.

Removed

• packages/react/src/SelectPanel/SelectPanel.test.tsx — removes a stale // jest function comment (the test below actually uses vi.fn()).

Rollout strategy

• Patch release
• Minor release
• Major release
• None

No public API surface changes. Existing Jest consumers continue to get real jest.fn() instances (detected via globalThis.jest.fn). New Vitest consumers get real vi.fn() instances. Non-test environments get no-ops, which is fine for the JSDOM polyfill use case.

Testing & Reviewing

• ✅ npx tsc -p packages/react/tsconfig.json --noEmit clean.
• ✅ npx prettier --check + npx eslint on changed files clean.
• ✅ SelectPanel.test.tsx runs cleanly (152 tests pass) — confirms the stale-comment removal didn't affect anything.
• The helper is @ts-nocheck (it's a globals/polyfill setup file), so types around the runtime-detect pattern aren't enforced, intentionally.

Worth a close look:

• The runtime-detect shape itself — there are a couple of reasonable variations:
  • globalThis.jest?.fn ?? globalThis.vi?.fn (current — Jest wins if both present, which matches the historical behaviour for Jest consumers).
  • Reverse order if we'd prefer Vitest to win when both are accidentally loaded (e.g. some pnpm hoisting edge cases).
• The fallback no-op for "no runtime" — it returns () => {}. Consumers without a test runtime importing this helper are an edge case (it's a test polyfill), but the no-op keeps the polyfill side-effects working.

Merge checklist

• Added/updated tests
• Added/updated documentation (changeset)
• Added/updated previews (Storybook)
• Changes are SSR compatible — the typeof document !== 'undefined' guard remains in place
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 1057c2d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[joshblack]

I'd be down to leave this one jest-specific since for vitest we'd be using browser mode, right? Or is that not the case? Ideally we wouldn't be shipping this file, I think.