feat(a11y): add extensible accessibility test infrastructure with axe-core" -m "- Add A11yChecker interface (types.ts) as the shared contract for accessibility checkers

packages/luna-charts/src/testing/a11y/checkers/axe-core.checker.ts

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+import axe from 'axe-core';
+import type { A11yChecker, A11yCheckResult } from './types';
+
+export const axeCoreChecker: A11yChecker = {
+  name: 'axe-core',
+
+  async run(rootElement: Element): Promise<A11yCheckResult> {
+    const results = await axe.run(rootElement);
+
+    return {
+      checkerName: 'axe-core',
+      violations: results.violations.map((violations) => ({
+        id: violations.id,
+        impact: violations.impact ?? null,
+        description: violations.help,
+        helpUrl: violations.helpUrl,
+        nodes: violations.nodes.map((node) => node.target.join(' ')),
+      })),
+    };
+  },
+};

packages/luna-charts/src/testing/a11y/checkers/types.ts

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+export interface A11yViolation {
+  id: string;
+  impact: 'minor' | 'moderate' | 'serious' | 'critical' | null;
+  description: string;
+  helpUrl?: string;
+  nodes: string[];
+}
+
+export interface A11yCheckResult {
+  checkerName: string;
+  violations: A11yViolation[];
+}
+
+export interface A11yChecker {
+  name: string;
+  run(root: Element): Promise<A11yCheckResult>;
+}

packages/luna-charts/src/testing/a11y/index.ts

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+import type { A11yChecker, A11yCheckResult } from './checkers/types';
+import { axeCoreChecker } from './checkers/axe-core.checker';
+
+const a11yCheckerRegistry: A11yChecker[] = [
+  axeCoreChecker,
+];
+
+export async function runA11yChecks(rootElement: Element): Promise<A11yCheckResult[]> {
+  return Promise.all(a11yCheckerRegistry.map((a11yChecker) => a11yChecker.run(rootElement)));
+}
+
+export type { A11yChecker, A11yCheckResult, A11yViolation } from './checkers/types';

packages/luna-charts/src/testing/a11y/matchers.ts

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+import { expect } from 'vitest';
+import type { A11yCheckResult } from './checkers/types';
+
+expect.extend({
+  toHaveNoA11yViolations(results: A11yCheckResult[]) {
+    const failing = results.filter((results) => results.violations.length > 0);
+
+    if (failing.length === 0) {
+      return {
+        pass: true,
+        message: () => 'expected accessibility violations, but none were found',
+      };
+    }
+
+    const message = failing
+      .map(
+        (results) =>
+          `[${results.checkerName}] ${results.violations.length} violation(s):\n` +
+          results.violations
+            .map((validation) => `  - ${validation.id} (${validation.impact}): ${validation.description}\n    affected: ${validation.nodes.join(', ')}`)
+            .join('\n')
+      )
+      .join('\n\n');
+
+    return {
+      pass: false,
+      message: () => `Accessibility violations found:\n\n${message}`,
+    };
+  },
+});
+
+declare module 'vitest' {
+  interface Assertion {
+    toHaveNoA11yViolations(): void;
+  }
+}