addon-a11y: re-export axe-core (e.g. @storybook/addon-a11y/axe-core) to scan an opened surface from a test

[unional]

Problem

@storybook/addon-a11y runs axe on document.body after a story and its tests finish. That covers a surface that is open at that moment, but there is no supported way to run the same check from inside a test, on one element, at the point the test has it open. A modal, sheet, popover or toast is closed when the story renders, so a test has to open it first.

To scan an opened surface explicitly (for example await expect(await findA11yViolations(dialog)).toEqual([])), a project has to import axe-core itself. axe-core is only a transitive dependency through the addon, so the project must add its own direct dependency and keep its version in step with the one the addon installs. Two copies of axe-core can also drift apart in version and rule set.

Proposal

Re-export axe-core from a subpath of the addon, for example:

import axe from '@storybook/addon-a11y/axe-core'

const { violations } = await axe.run(dialog, { rules })

This keeps one axe-core version, the one the addon is tested with, and needs no extra dependency.

Alternatives

• A small helper that runs the addon's own run() with its configuration (parameters.a11y.config and options, plus the rules the addon always disables) against a given element, and returns the results. This would be the better fit if you prefer not to expose axe-core directly, because the rule configuration would then match what the addon applies automatically.
• Documenting a11y.context with include: 'body' as the way to cover portals. That does not help with scanning at a chosen moment, or with tying a violation to one surface.

Happy to send a PR for the re-export if the subpath approach is acceptable.