chore: WIP React 17 upgrade and add regression test suite

[bosun-ai]

Summary

Work in progress to upgrade React from 3.1.15 to 17.0.2. This PR also introduces a basic regression test suite to support the upgrade effort.

Scope of changes

• Add regression testing setup with Jest, React Testing Library (RTL), and MSW.
  • Added regression-tests/jest.config.js with jsdom environment and Babel transform for js/jsx.
  • Added regression-tests/setupTests.js to configure jest-dom, polyfills, and MSW server lifecycle.
  • Added regression-tests/loading.test.js with a passing test for the Loading component.
• Project configuration updates:
  • Added .yarnrc.yml (nodeLinker: node-modules) and .yarn/install-state.gz.
  • Added .nvmrc to specify Node 12 for local development consistency.
  • Updated devDependencies in package.json to include @testing-library/react, @testing-library/jest-dom, and msw.

Regression test suite

A minimal regression suite has been added to verify core UI behavior during the React upgrade.

• Tooling: Jest + React Testing Library (RTL) + MSW
• Current coverage: Loading component renders successfully within themed context
• Run instructions:
  npm run jest -- --config regression-tests/jest.config.js --runInBand

Reasoning and impact

• Establishes a foundation for regression tests to detect breaking changes as React is upgraded to 17.0.2.
• Ensures basic rendering and theming continue to work (Loading component) while the upgrade proceeds.

Risks

• Test environment and polyfills may require adjustment once React 17 upgrade changes land across the app.
• MSW handlers are minimal; additional API mocks may be needed for broader coverage.

Follow-ups and reviewer call-outs

• Expand regression coverage to additional components and flows impacted by the React upgrade.
• Confirm Node version alignment (currently .nvmrc: 12) with CI and deployment environments.
• Validate Babel/Jest config compatibility once React 17 and associated dependencies are updated.

Notes

• This PR is a work in progress and is not intended to be merged yet.
• This is a test PR and should not be merged.

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This pull request is created by bosun, a code maintenance automation platform. For more information, visit bosun.ai.