[React 19] revive `react-test-renderer`

## Summary Ideally `react` is shipped with official test utilities instead of relying on third-party vendors. Unfortunately it was decided to deprecate`react-test-renderer`. As a consequence it isn't easy anymore to: - write unit tests - test React components independently of the target platform ([React DOM](https://legacy.reactjs.org/docs/react-dom.html), [React Native](https://reactnative.dev/), or any other [**custom renderer**](https://github.com/chentsulin/awesome-react-renderer) which is out there) - test complex, deeply nested component trees - shallow render - make shallow snapshots - to run tests FAST (in memory) ## Regressions `@testing-library/react` is an integration testing library, promotes testing anti-patterns and completely ditches unit tests. It is **slow** and requires a DOM or a mock like `js-dom`. Please refer to these resources for a comprehensive understanding of why unit tests are of high value: - https://martinfowler.com/articles/practical-test-pyramid.html#UnitTests ### Other critical voices from the community - https://javascript.plainenglish.io/in-defense-of-shallow-rendering-5f627f7c155d - https://blog.hao.dev/my-struggles-with-react-testing-library ## References > `react-test-renderer` is deprecated. A warning will fire whenever calling `ReactTestRenderer.create()` or `ReactShallowRender.render()`. The `react-test-renderer` package will remain available on NPM but will not be maintained and may break with new React features or changes to React’s internals. https://react.dev/warnings/react-test-renderer > `react-test-renderer` is deprecated and no longer maintained. It will be removed in a future version. As of React 19, you will see a console warning when invoking `ReactTestRenderer.create()`. https://www.npmjs.com/package/react-test-renderer/v/19.0.0-canary-8afa144bd-20240416?activeTab=readme#react-test-renderer-deprecated **Note:** that affects any code using `react-test-renderer` https://github.com/search?q=repo%3Ajestjs%2Fjest%20re…