Add tests for the theme helper and ThemeToggle component

[mikewheeleer]

Test the theme helpers and ThemeToggle behaviour

Description

src/lib/theme.ts (read/write/effective theme with matchMedia) and src/components/ThemeToggle.tsx (which toggles the dark class on documentElement) have no tests. Regressions here silently break dark mode across every page. This issue adds coverage for both.

Requirements and context

• Repository scope: Agentpay-Org/Agentpay-frontend only.
• For theme.ts: assert readTheme validates the stored value, writeTheme persists, and effectiveTheme("system") follows a mocked matchMedia.
• For ThemeToggle: mock localStorage and matchMedia, assert the three buttons render, aria-pressed reflects the active theme, and clicking toggles documentElement.classList.
• Stub window.matchMedia in the test setup since jsdom lacks it.

Suggested execution

• Fork the repo and create a branch
• git checkout -b test/testing-17-theme
• Implement changes
  • Write comprehensive tests in: create src/lib/__tests__/theme.test.ts and src/components/__tests__/ThemeToggle.test.tsx.
  • Add documentation: if you add a matchMedia polyfill, note it in jest.setup.ts.
  • Validate the role="group" with aria-label="Theme" is reachable.
• Test and commit

Test and commit

• Run npm run lint, npm run typecheck, and npm test.
• Cover edge cases: invalid stored value coerced to system, SSR guards (typeof window === "undefined"), and dark-preference media query.
• Include the npm test output and coverage for the two modules.

Example commit message

test(theme): cover theme helpers and ThemeToggle dark-mode wiring

Guidelines

• Minimum 95 percent test coverage for the impacted modules.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the AgentPay community on Discord for questions, reviews, and faster merges: https://discord.gg/eXvRKkgcv
• ⭐ This is a GrantFox OSS / Official Campaign task and may be rewarded. When your PR is merged you'll be prompted to rate the project — if this issue and the maintainers helped you ship, we'd be grateful for a 5-star rating. Clear questions in Discord and tidy, well-tested PRs are the fastest path to a merge and a reward.

[Senorespecial]

I would like to work on this issue, please assign

[barry01-hash]

I would love to work on this project.
Please approve

[Errordog2]

/attempt #16

Submitted PR: #33

What changed:

• Added focused tests for theme storage validation, persistence, and system preference resolution.
• Added ThemeToggle tests for rendered options, active �ria-pressed state, localStorage persistence, and dark-class toggling.
• Mocked window.matchMedia in the tests for jsdom coverage.

Validation:

• Kept tests within the existing Jest/Testing Library setup and added no new runtime dependencies.
• Could not run the full dependency-backed test suite locally because the repo clone/install path was blocked by network resets; the PR is intentionally test-only and should run in repository CI.