Testing Strategy Skill
Decision frameworks for accessibility testing — when to use automated tools vs. manual testing, which screen reader + browser combinations to test, and how to write accessibility acceptance criteria.
Automated vs. Manual Testing Coverage
| What Automated Tools Catch (~30-40%) | What Requires Manual Testing (~60-70%) |
|---|
| Missing alt text on images | Alt text quality and accuracy |
| Missing form labels | Label clarity and helpfulness |
| Color contrast ratios (computed) | Color contrast in context (gradients, images) |
| Missing lang attribute | Correct language identification |
| Duplicate IDs | Logical reading order |
| Missing ARIA roles on custom widgets | Correct ARIA role for the interaction pattern |
| Heading hierarchy violations | Heading text meaningfulness |
| Empty links and buttons | Link/button text descriptiveness |
| Missing table headers | Table caption and header association quality |
| Syntax errors in ARIA | Screen reader announcement correctness |
Browser + Screen Reader Compatibility Matrix
Primary Test Combinations (Required)
| Screen Reader | Browser | OS | Priority |
|---|
| NVDA | Firefox | Windows | Must test |
| NVDA | Chrome | Windows | Must test |
| JAWS | Chrome | Windows | Must test |
| VoiceOver | Safari | macOS | Must test |
| VoiceOver | Safari | iOS | Must test |
| TalkBack | Chrome | Android | Should test |
Secondary (Nice to Have)
| Screen Reader | Browser | OS |
|---|
| Narrator | Edge | Windows |
| JAWS | Edge | Windows |
Testing Decision Tree
Is it a new component or page?
├── Yes → Full test coverage (automated + manual)
│ ├── Run axe-core / Lighthouse scan
│ ├── Keyboard-only navigation test
│ ├── Screen reader announcement test (NVDA + VoiceOver minimum)
│ └── Visual check at 200% zoom
└── No → What changed?
├── Colors/styling → Contrast check + visual review
├── Interactive behavior → Keyboard + screen reader test
├── Content/text → Screen reader announcement check
├── Layout/order → Reading order + focus order test
└── Dependencies updated → Regression scan (axe-core)
Regression Testing Patterns
CI Pipeline Accessibility Gates
- axe-core scan: Run on every PR. Fail on new critical/serious violations.
- Baseline management: Store known issues in
.a11y-baseline.json. Only fail on new issues.
- Lighthouse score threshold: Set minimum accessibility score (e.g., 90). Fail on regression.
- Visual regression: Capture screenshots at 200% zoom. Compare for focus indicator and layout changes.
Preventing Regressions
- Add accessibility assertions to existing component tests (see
testing-accessibility.instructions.md)
- Include keyboard navigation in E2E test suites
- Track accessibility score trends over time (not just pass/fail)
Acceptance Criteria Template
For User Stories
Given [context],
When [action by keyboard/mouse/screen reader],
Then [accessible outcome]:
- [ ] Component has an accessible name (via label, aria-label, or aria-labelledby)
- [ ] Component has the correct ARIA role
- [ ] Component is reachable and operable by keyboard (Tab, Enter, Space, Escape, Arrows as appropriate)
- [ ] Focus is visible when the component receives focus
- [ ] State changes are announced to screen readers (aria-expanded, aria-selected, aria-checked, etc.)
- [ ] Error messages are associated with their inputs (aria-describedby or aria-errormessage)
- [ ] Content is readable at 200% zoom without horizontal scrolling
- [ ] Color is not the only means of conveying information
Common Testing Tools
| Tool | Type | Best For |
|---|
| axe-core / @axe-core/cli | Automated | CI/CD integration, broad violation scan |
| Lighthouse | Automated | Performance + accessibility combined score |
| WAVE | Semi-automated | Visual overlay of accessibility features/issues |
| Accessibility Insights | Semi-automated | FastPass (automated) + Assessment (guided manual) |
| pa11y | Automated | CI/CD, HTML CodeSniffer rules |
| jest-axe | Unit test | Component-level axe scans in jest |
| cypress-axe | E2E test | Page-level axe scans in Cypress |
| playwright + @axe-core/playwright | E2E test | Page-level axe scans in Playwright |
Screen Reader Testing Quick Reference
NVDA (Windows)
| Key | Action |
|---|
| Insert + Space | Toggle focus/browse mode |
| Tab | Move to next focusable element |
| H | Next heading |
| D | Next landmark |
| F | Next form field |
| T | Next table |
| Insert + F7 | Elements list (links, headings, landmarks) |
VoiceOver (macOS)
| Key | Action |
|---|
| VO (Ctrl+Option) + Right | Move to next element |
| VO + Space | Activate current element |
| VO + U | Open rotor (navigate by type) |
| VO + Cmd + H | Next heading |