[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 deprecatereact-test-renderer.

As a consequence it isn't easy anymore to:

• write unit tests
• test React components independently of the target platform (React DOM, React Native, or any other custom 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react-test-renderer is deprecated and no longer maintained.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