[Bl1ckxy]

Closes #206

What and why

Sets up component testing infrastructure so future component fixes (like the invoice reset in #201 or the hydration error in #193) can ship with tests that fail before the fix.

Previously, vitest.config.ts ran all tests in the node environment and only picked up lib/**/*.test.ts. There was no DOM library or Testing Library in package.json, so component bugs could not be caught by tests.

This PR adds happy-dom and @testing-library/react as dev dependencies, configures Vitest 4 test.projects to split environments, and includes a proof-of-concept test for CopyButton.

Changes

• package.json: Added happy-dom, @testing-library/react, @testing-library/dom as devDependencies
• vitest.config.ts: Replaced flat test.environment/test.include with test.projects array:
  • lib project → node environment, lib/**/*.test.ts (unchanged behavior)
  • components project → happy-dom environment, components/**/*.test.tsx + app/**/*.test.tsx
  • Added resolve.alias to each project (Vitest 4 projects don't inherit root config)
• vitest.setup.ts (new): Imports @testing-library/jest-dom/vitest for DOM matchers
• components/shared/CopyButton.test.tsx (new): Tests that clicking the button calls navigator.clipboard.writeText with the correct value and the label changes to "Copied"

How I tested this

• npm run test → 18 test files, 444 tests, all passing (443 lib + 1 component)
• Verified lib tests still run in node environment
• Verified CopyButton test fails when navigator.clipboard.writeText is removed from the component
• npm run lint → passes
• npm run build → passes

AI assistance

Used an AI assistant (Claude) to research Vitest 4 test.projects environment splitting, debug why happy-dom's navigator.clipboard can't be overridden with Object.assign, and draft the CopyButton component test. Every line of code in this PR was written and verified by me — npm run test passes 444/444, npm run lint and npm run build pass.

Type of change

• Bug fix
• New tool or feature
• Tests
• Refactor or cleanup
• Docs

Checklist

• I was assigned the linked issue
• npm run lint && npm run test && npm run build passes locally
• Logic changes live in lib/ and have a test in lib/tests/
• For a bug fix: the new test fails without my change
• No analytics, trackers, or calls that send user data off-device
• Works in both light and dark themes (if UI changed)
• Inputs have labels and it works with the keyboard alone (if UI changed)
• New tool: registry entry, page.tsx, client component, opengraph-image.tsx, and the bug report dropdown are all done

Notes for reviewers

• The resolve.alias duplication in each project is required because Vitest 4 test.projects override rather than inherit the root config. Without it, @/lib/... imports fail in both projects.
• The clipboard mock uses Object.defineProperty instead of Object.assign because happy-dom defines navigator.clipboard as a getter-only property.
• CONTRIBUTING.md already documents the component test location (line added previously), so no doc changes were needed.

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[anurag629]

Thanks @Bl1ckxy, this is what #206 asked for. The lib/ tests still run in node, the components project picks up CopyButton.test.tsx in happy-dom, and the test fails when I replace the writeText call. The lockfile only adds the new packages. Lint, all 444 tests, the build and the page check pass on top of develop.

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