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Based on - https://github.com/facebook/react/pull/28497 - https://github.com/facebook/react/pull/28419 Reusing the disableLegacyMode flag, we set ReactTestRenderer to always render with concurrent root where legacy APIs are no longer available. If disableLegacyMode is false, we continue to allow the unstable_isConcurrent option determine the root type. Also checking a global `IS_REACT_NATIVE_TEST_ENVIRONMENT` so we can maintain the existing behavior for RN until we remove legacy root support there.
react-test-renderer
This package provides an experimental React renderer that can be used to render React components to pure JavaScript objects, without depending on the DOM or a native mobile environment.
Essentially, this package makes it easy to grab a snapshot of the "DOM tree" rendered by a React DOM or React Native component without using a browser or jsdom.
Documentation:
https://reactjs.org/docs/test-renderer.html
Usage:
const ReactTestRenderer = require('react-test-renderer');
const renderer = ReactTestRenderer.create(
<Link page="https://www.facebook.com/">Facebook</Link>
);
console.log(renderer.toJSON());
// { type: 'a',
// props: { href: 'https://www.facebook.com/' },
// children: [ 'Facebook' ] }
You can also use Jest's snapshot testing feature to automatically save a copy of the JSON tree to a file and check in your tests that it hasn't changed: https://jestjs.io/blog/2016/07/27/jest-14.html.