Add date-picker-calendar test case (interaction-level selection-grid ARIA)

[manichandra]

Summary

Adds a new test case, test_cases/date-picker-calendar/, that evaluates a date-picker
calendar widget. It focuses on the interaction-level ARIA contract for selection grids
— semantics that a static axe-core pass does not catch on its own.

Motivation

The existing test cases cover forms and disclosure patterns, but there is no calendar /
date-picker case. Date grids are a common pattern models frequently get subtly wrong in
ways axe-core alone does not flag:

• aria-pressed vs aria-selected. Generated calendars often mark the chosen day with
  aria-pressed (toggle-button state) instead of aria-selected (selection state). Both
  attributes are individually valid, so axe-core does not report it — but a screen reader
  announces "button pressed" instead of "selected". A role-contract defect only a semantics
  assertion catches.
• Missing grid/listbox semantics. Day cells are often plain buttons with no
  role="gridcell"/role="grid", so AT cannot present them as selectable days.
• No keyboard navigation. Calendars frequently ship without arrow-key movement.

These map to WAI-ARIA 1.2, the WAI-ARIA APG grid pattern, and WCAG 2.1 SC 4.1.2.

What this adds

• prompt.yaml — a neutral product spec (does not state the ARIA answer).
• test.js — six assertions, following the existing
  module.exports.run = async ({ page, assert, utils }) convention:
  1. Day grid present and openable
  2. Each day cell has an accessible name
  3. Day cells expose grid/listbox selection semantics
  4. Selection uses aria-selected, not aria-pressed
  5. Exactly one day marked selected after a choice
  6. Arrow keys move focus within the grid

DOM discovery is self-contained; the only utils call (reload) is guarded.

Validation

Ran test.js with Playwright against a conformant calendar (all six pass) and an
anti-pattern calendar using aria-pressed toggle buttons with no grid semantics or
keyboard nav (assertions 3–6 fail with specific messages).

Checklist

• I have signed the Microsoft CLA
• [ x] I ran the repository's evaluation harness locally
• [ x] The new case follows the existing test_cases/ conventions

[manichandra]

@microsoft-github-policy-service agree