test: add regression test suite scaffolding for React upgrade (WIP)

[bosun-ai]

Summary

• Set up a standalone regression test suite to validate React upgrade work in a controlled environment. This PR is work in progress; no functional app changes are included yet.

Scope of changes

• Added an isolated Jest + jsdom test workspace under regression-tests/ to exercise minimal React rendering and interactions without JSX/Babel.
• Introduced MSW scaffolding to mock network calls and cross-fetch to enable fetch in Node.
• Added npm script test:regression to run the suite.
• Project config additions (.nvmrc, .yarnrc.yml) to standardize local environment; yarn.lock updated accordingly.

React upgrade context

• Goal: upgrade react from ^16.8.4 to 17.0.2. This PR prepares the regression test harness to safely validate behavior during the upgrade.
• Current working dependency set in the regression workspace uses React 16.14 to establish baseline tests before incrementally moving to 17.0.2.

Regression test suite setup

• Regression test suite added and passing. You can run it via npm run test:regression.

Highlights:

• Isolated test workspace regression-tests/ with Jest + jsdom + Testing Library + MSW.
• Minimal React tests using React.createElement() to avoid JSX/Babel.
• cross-fetch installed to support fetch and MSW in Node.
• Jest-dom matcher registration fixed by requiring extend-expect.

Run:

• npm run test:regression

Working dependency versions:

• react: ^16.14.0
• react-dom: ^16.14.0
• jest: ^26.6.3
• jest-environment-jsdom: ^26.6.2
• @testing-library/react: ^12.1.5
• @testing-library/jest-dom: ^5.16.5
• msw: ^0.49.3
• cross-fetch: ^4.1.0

Files touched:

• regression-tests/jest.config.js
• regression-tests/setupTests.js
• regression-tests/handlers.js
• regression-tests/server.js
• regression-tests/simple.test.js
• package.json (added test:regression script)
• .nvmrc, .yarnrc.yml, yarn.lock

Notes:

• Jest prints a validation warning about setupFilesAfterEnv under this config but tests pass. I explicitly require jest-dom in the test to guarantee matcher availability on Jest 26.
• MSW server scaffolding is ready; add handlers in regression-tests/handlers.js as you expand tests.

Impact and risk

• Low risk; changes are limited to test scaffolding and configuration. No runtime code paths are modified.

Follow-up work

• Incrementally bump the regression workspace React and React DOM to 17.0.2, adjust tests as needed, and then roll changes into the main app dependencies.
• Add representative components and network interactions to the regression suite to cover critical paths.
• Evaluate removing explicit jest-dom registration after upgrading Jest.

Reviewer action items

• Run npm install and npm run test:regression to verify the suite passes locally.
• Confirm test workspace structure and config meet project expectations.
• Provide feedback on additional scenarios to include in the regression suite.

Links

• This is a test PR and should not be merged.

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