952aa74f8e
Instead of createElement. We should have done this when we initially released jsx-runtime but better late than never. The general principle is that our tests should be written using the most up-to-date idioms that we recommend for users, except when explicitly testing an edge case or legacy behavior, like for backwards compatibility. Most of the diff is related to tweaking test output and isn't very interesting. I did have to workaround an issue related to component stacks. The component stack logic depends on shared state that lives in the React module. The problem is that most of our tests reset the React module state and re-require a fresh instance of React, React DOM, etc. However, the JSX runtime is not re-required because it's injected by the compiler as a static import. This means its copy of the shared state is no longer the same as the one used by React, causing any warning logged by the JSX runtime to not include a component stack. (This same issue also breaks string refs, but since we're removing those soon I'm not so concerned about that.) The solution I went with for now is to mock the JSX runtime with a proxy that re-requires the module on every function invocation. I don't love this but it will have to do for now. What we should really do is migrate our tests away from manually resetting the module state and use import syntax instead.
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.