Add unit tests with Jest and React Testing Library

[bigweavergammainternal]

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Summary

This PR implements a comprehensive unit testing infrastructure for the amplify-next-template Next.js application using Jest and React Testing Library.

Changes

Testing Framework Setup:

• Added Jest configuration (jest.config.ts) with Next.js integration using next/jest
• Configured jsdom test environment for React component testing
• Set up module path aliasing (@/*) to match the project's TypeScript configuration
• Added Jest setup file (jest.setup.ts) with @testing-library/jest-dom matchers
• Updated tsconfig.json to include test files in TypeScript compilation

App Component Tests (__tests__/app/page.test.tsx):

• Added rendering tests for the main heading, "new" button, success message, and tutorial link
• Implemented tests for listTodos function behavior including:
  • Subscription initialization via observeQuery on mount
  • State updates when subscription receives todo data
  • Handling empty todo lists from subscription
  • Handling subscription updates with new todos
• Implemented tests for createTodo function behavior including:
  • Prompt opening when "new" button is clicked
  • Creating todos with user-entered content
  • Handling cancelled prompts (null content)
  • Handling empty string input
• Added user interaction tests for multiple todo creations

RootLayout Component Tests (__tests__/app/layout.test.tsx):

• Added rendering tests for children, HTML lang attribute, and Inter font className
• Implemented structure tests for HTML document hierarchy
• Added metadata export tests for title and description

Amplify Backend Configuration Tests:

• Added auth resource tests (__tests__/amplify/auth.resource.test.ts) for email login configuration
• Added data resource tests (__tests__/amplify/data.resource.test.ts) for:
  • Schema configuration with Todo model
  • Authorization modes (apiKey with 30-day expiration)
  • Schema type exports

Package Dependencies:

• Added @testing-library/jest-dom for extended DOM matchers
• Added @testing-library/react for React component testing
• Added @types/jest for TypeScript type definitions
• Added jest, jest-environment-jsdom, and ts-jest for test execution

NPM Scripts:

• Added test script for running tests
• Added test:watch script for watch mode
• Added test:coverage script for coverage reports

Impact Assessment

• Establishes testing infrastructure for ongoing development quality assurance
• Follows React Testing Library best practices with proper mocking of Amplify dependencies
• Enables CI/CD integration with Jest test runner

Testing

• All unit tests pass successfully
• Tests are isolated with proper mocking of external dependencies (aws-amplify, next/font)

[This description was generated by Claude]