Sebastian Markbåge
a5297ece62
Starting a View Transition is an async sequence. Since React can get a sync update in the middle of sequence we sometimes interrupt that sequence. Currently, we don't actually cancel the View Transition so it can just run as a partial. This ensures that we fully skip it when that happens, as well as warn. However, it's very easy to trigger this with just a setState in useLayoutEffect right now. Therefore if we're inside the preparing sequence of a startViewTransition, this delays work that would've normally flushed in a microtask. ~Maybe we want to do the same for Default work already scheduled through a scheduler Task.~ Edit: This was already done. `flushSync` currently will still lead to an interrupted View Transition (with a warning). There's a tradeoff here whether we want to try our best to preserve the guarantees of `flushSync` or favor the animation. It's already possible to suspend at the root with `flushSync` which means it's not always 100% guaranteed to commit anyway. We could treat it as suspended. But let's see how much this is a problem in practice.
react-test-renderer (DEPRECATED)
Deprecation notice
react-test-renderer is deprecated and no longer maintained.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().
React Testing
This library creates a contrived environment and its APIs encourage introspection on React's internals, which may change without notice causing broken tests. It is instead recommended to use browser-based environments such as jsdom and standard DOM APIs for your assertions.
The React team recommends @testing-library/react as a modern alternative that uses standard APIs, avoids internals, and promotes best practices.
React Native Testing
The React team recommends @testing-library/react-native as a replacement for react-test-renderer for native integration tests. This React Native testing-library variant follows the same API design as described above and promotes better testing patterns.
Documentation
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.