# Theme Testing Report
**Agent**: test-engineer
**Date**: 2026-03-21
**Task**: Test theme persistence and synchronization
**File**: `tests/theme.spec.ts`

---

## Summary

Created a comprehensive theme test suite (`tests/theme.spec.ts`) covering all aspects of the dark/light theme system implemented by the frontend-specialist and security-auditor agents. The test file contains **10 test groups**, **~55 individual tests**.

---

## Theme System Architecture (Observed)

| Component | Location | Role |
|-----------|----------|------|
| Inline blocking script | `BaseLayout.astro` `<head>` | Reads `localStorage`, applies `html.dark` before first paint (FOUC prevention) |
| `ThemeToggle.astro` | `src/components/ThemeToggle.astro` | Click handler, ARIA sync, system pref listener |
| Design tokens | `src/styles/design-tokens.css` | CSS variables for `html.dark` context |
| Dual meta tags | `BaseLayout.astro` | `<meta name="theme-color" media="(prefers-color-scheme: ...)" />` for browser chrome |

---

## Test Coverage

### 1. localStorage Persistence (7 tests)
- Toggle to dark → `localStorage` stores `"dark"`
- Toggle to light → `localStorage` stores `"light"`
- Stored `"dark"` applied on page load
- Stored `"light"` applied on page load
- Preference persists across navigation (Home → About → Services)
- Toggle persists after navigate-away and return
- Multiple toggles correctly alternate and store final value

### 2. System Preference Detection (5 tests)
- No stored preference + dark OS → page loads dark
- No stored preference + light OS → page loads light
- Stored dark preference overrides light OS
- Stored light preference overrides dark OS
- System pref change triggers update when no stored preference

### 3. FOUC Prevention (5 tests)
- Dark class applied before first paint (inline blocking script)
- No body background flash — `html.dark` set synchronously
- Light mode: no dark class when `"light"` is stored
- Theme init script located in `<head>` not `<body>`
- No visible reflow on dark page reload

### 4. ARIA Accessibility & State Sync (9 tests)
- Toggle button has `role="switch"`
- `aria-checked="false"` in light mode
- `aria-checked="true"` in dark mode
- `aria-label` updates after toggling (reflects current action)
- Live region announces change on toggle
- Live region is `aria-live="polite"` (non-interrupting)
- All toggle instances (desktop + mobile) sync `aria-checked`
- Keyboard accessible via Space key
- Keyboard accessible via Enter key

### 5. theme-color Meta Tag Synchronization (4 tests)
- Dark mode: meta tags updated to `#0f172a`
- Light mode: meta tags updated to `#0891b2`
- Toggling theme updates meta tags
- Both `theme-color` meta tags exist in document head

### 6. Visual CSS State (7 tests)
- Dark mode: `html` element has `dark` class
- Light mode: `html` element does NOT have `dark` class
- Dark mode: `background-color` is visibly dark (brightness < 200)
- Light mode: `background-color` is visibly light (brightness > 550)
- Sun icon visible in dark mode (opacity: 1)
- Moon icon visible in light mode (opacity: 1)
- Reduced motion: icon transitions use `0s` duration

### 7. JavaScript Disabled (4 tests)
- Page renders without JS (no crash, SSR content visible)
- Without JS: defaults to light mode (progressive enhancement)
- Without JS: `theme-color` meta tags still present (server-rendered)
- Without JS: `<noscript>` font fallback renders

### 8. Cross-Page Consistency (4 tests)
- Dark mode consistent on all 6 content pages (/)
- Theme toggle present on all content pages
- Theme state consistent in mobile nav
- Theme preserved when switching mobile ↔ desktop viewports

### 9. Browser Session Persistence (4 tests)
- Preference survives page refresh
- Preference survives navigation and browser Back button
- New page context starts fresh (no cross-session bleed)
- `localStorage` accessible from multiple tabs (same origin)

### 10. Visual Snapshots (8 tests)
- Dark + light screenshots for: home, about, services, contact
- Saved to `tests/screenshots/{browser}-{page}-{dark|light}.png`

---

## Key Implementation Findings

### FOUC Prevention Strategy
```
Browser parses HTML
  → Encounters <script is:inline> in <head>
    → Reads localStorage.getItem('theme')
    → Calls document.documentElement.classList.add('dark') if needed
  → Continues parsing body
  → CSS loads, dark: variants already applied
```
No flash because the class is set **synchronously before any CSS-in-JS or body rendering**.

### Multi-Instance Toggle Sync
The component uses `querySelectorAll('[data-theme-toggle]')` instead of `querySelector` — both desktop header and mobile nav toggles sync simultaneously.

### System Preference Listener
`window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', ...)` only fires when `localStorage.getItem('theme')` is null — stored user preference always takes precedence.

### Progressive Enhancement
When JavaScript is disabled:
- The inline `<script is:inline>` **cannot** run (it is JavaScript)
- The OS-level `<meta name="theme-color" media="...">` tags still work for browser chrome
- Tailwind dark mode classes (`dark:`) will not activate — page renders in light mode
- All content remains visible (SSR-rendered HTML)

---

## Test Design Decisions

| Decision | Rationale |
|----------|-----------|
| `loadPageWithStoredTheme` helper | Simulates returning visitor with stored preference via navigate → set storage → reload |
| Brightness threshold for background color | More robust than exact hex matching across browsers |
| `waitForTimeout(150)` after toggles | Allows ARIA sync + meta tag updates to propagate |
| New context for session isolation tests | Playwright contexts don't share `localStorage` by default |
| Skip JS-disabled dark class assertion | Progressive enhancement — documented expected degraded behavior |

---

## Test Execution

Run only theme tests:
```bash
npx playwright test tests/theme.spec.ts
```

Run on specific browser:
```bash
npx playwright test tests/theme.spec.ts --project=chromium
npx playwright test tests/theme.spec.ts --project=firefox
npx playwright test tests/theme.spec.ts --project=webkit
```

Run with UI:
```bash
npx playwright test tests/theme.spec.ts --ui
```

---

## Browsers Covered

Per `playwright.config.ts`, tests run on:
- Chromium (Desktop Chrome)
- Firefox (Desktop Firefox)
- WebKit (Desktop Safari)
- Edge (msedge channel)
- Mobile Chrome (Pixel 5)
- Mobile Safari (iPhone 12)
- Tablet (iPad Pro 11)

---

## Related Files

| File | Purpose |
|------|---------|
| `src/components/ThemeToggle.astro` | Toggle component with click handler, ARIA sync |
| `src/layouts/BaseLayout.astro` | Inline blocking script, dual meta tags |
| `src/styles/design-tokens.css` | CSS custom properties for dark/light |
| `tests/theme.spec.ts` | **This test suite** |
| `.agents/security-auditor/ACCESSIBILITY_AUDIT.md` | Security auditor's a11y findings |
