Add unit tests for Amplify Next.js template

[ghostyappbeta]

This pull request was generated by @kiro-agent 👻

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Summary

Adds a comprehensive unit test suite for the Amplify Next.js template repository using Node.js 22's built-in test runner (node:test). No external testing dependencies are required.

Changes

• 6 test files with 30 passing tests covering all source modules
• Added test script to package.json
• Tests cover:
  • amplify/auth/resource.ts — verifies auth configuration with email login
  • amplify/data/resource.ts — verifies data schema definition and authorization rules
  • amplify/backend.ts — verifies backend configuration imports and structure
  • app/layout.tsx — verifies metadata, root layout exports, and HTML structure
  • app/page.tsx — verifies client directive, Amplify configuration, todo CRUD operations, and component structure
  • next.config.js — verifies Next.js configuration export

Testing Approach

• Module mocking with mock.module() for pure .ts Amplify resource files — tests actual module behavior by mocking @aws-amplify/backend
• Structural analysis via readFileSync for .tsx files — verifies code correctness without needing a JSX parser
• Direct require() for next.config.js

How to run

npm test

Notes

• Uses Node.js built-in --experimental-strip-types and --experimental-test-module-mocks flags
• Zero additional npm dependencies needed