react-test-renderer

What is react-test-renderer?

The react-test-renderer package is designed for testing React components in a more efficient and lightweight manner. It provides a renderer that can be used to render React components into pure JavaScript objects without depending on the DOM or a native mobile environment. This makes it ideal for testing components in isolation from the browser or any other external environment.

What are react-test-renderer's main functionalities?

Rendering components to JSON

This feature allows you to render a React component and generate a JSON output of the rendered component. This is useful for snapshot testing, where you can compare the current version of the component with a previously stored snapshot.

import React from 'react';
import renderer from 'react-test-renderer';
const component = renderer.create(<MyComponent />);
let tree = component.toJSON();
expect(tree).toMatchSnapshot();

Testing component output

This feature enables testing of the component's output. You can inspect the rendered component to verify that it has the expected props, state, or behavior. This is useful for ensuring that your component behaves correctly under various conditions.

import React from 'react';
import renderer from 'react-test-renderer';
const component = renderer.create(<MyComponent prop='value' />);
const instance = component.root;
expect(instance.props.prop).toBe('value');

Interacting with component instances

This feature allows you to interact with the component instances directly. You can simulate events or call methods on the component instance and then re-render. This is useful for testing the component's behavior in response to user interactions or lifecycle events.

import React from 'react';
import renderer from 'react-test-renderer';
class MyComponent extends React.Component {
  state = { clicked: false };
  handleClick = () => {
    this.setState({ clicked: true });
  };
  render() {
    return (<button onClick={this.handleClick}>Click me</button>);
  }
}
const component = renderer.create(<MyComponent />);
const button = component.root.findByType('button');
button.props.onClick();
expect(component.toJSON()).toMatchSnapshot();

Other packages similar to react-test-renderer

enzyme

Enzyme is a popular testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output. Unlike react-test-renderer, Enzyme allows you to simulate events and provides a more jQuery-like API for selecting elements. However, it requires an adapter to work with different versions of React.

react-testing-library

React Testing Library is a set of helpers that let you test React components without relying on their implementation details. This approach encourages better testing practices by focusing on the behavior of components rather than their internal structure. It's more aligned with user interaction compared to react-test-renderer, which is more about rendering components to JSON for snapshot testing.

README

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.

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: http://facebook.github.io/jest/blog/2016/07/27/jest-14.html.

Changelog

16.0.0 (September 26, 2017)

New JS Environment Requirements

• React 16 depends on the collection types Map and Set, as well as requestAnimationFrame. If you support older browsers and devices which may not yet provide these natively (e.g. <IE11), you may want to include a polyfill.

New Features

• Components can now return arrays and strings from render. (Docs coming soon!)
• Improved error handling with introduction of "error boundaries". Error boundaries are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of the component tree that crashed.
• First-class support for declaratively rendering a subtree into another DOM node with ReactDOM.createPortal(). (Docs coming soon!)
• Streaming mode for server side rendering is enabled with ReactDOMServer.renderToNodeStream() and ReactDOMServer.renderToStaticNodeStream(). (@aickin in #10425, #10044, #10039, #10024, #9264, and others.)
• React DOM now allows passing non-standard attributes. (@nhunzaker in #10385, 10564, #10495 and others)

Breaking Changes

• There are several changes to the behavior of scheduling and lifecycle methods:
  • ReactDOM.render() and ReactDOM.unstable_renderIntoContainer() now return null if called from inside a lifecycle method.
    • To work around this, you can either use the new portal API or refs.
  • Minor changes to setState behavior:
    • Calling setState with null no longer triggers an update. This allows you to decide in an updater function if you want to re-render.
    • Calling setState directly in render always causes an update. This was not previously the case. Regardless, you should not be calling setState from render.
    • setState callback (second argument) now fires immediately after componentDidMount / componentDidUpdate instead of after all components have rendered.
  • When replacing <A /> with <B />, B.componentWillMount now always happens before A.componentWillUnmount. Previously, A.componentWillUnmount could fire first in some cases.
  • Previously, changing the ref to a component would always detach the ref before that component's render is called. Now, we change the ref later, when applying the changes to the DOM.
  • It is not safe to re-render into a container that was modified by something other than React. This worked previously in some cases but was never supported. We now emit a warning in this case. Instead you should clean up your component trees using ReactDOM.unmountComponentAtNode. See this example.
  • componentDidUpdate lifecycle no longer receives prevContext param. (@bvaughn in #8631)
  • Non-unique keys may now cause children to be duplicated and/or omitted. Using non-unique keys is not (and has never been) supported, but previously it was a hard error.
  • Shallow renderer no longer calls componentDidUpdate() because DOM refs are not available. This also makes it consistent with componentDidMount() (which does not get called in previous versions either).
  • Shallow renderer does not implement unstable_batchedUpdates() anymore.
  • ReactDOM.unstable_batchedUpdates now only takes one extra argument after the callback.
• The names and paths to the single-file browser builds have changed to emphasize the difference between development and production builds. For example:
  • react/dist/react.js → react/umd/react.development.js
  • react/dist/react.min.js → react/umd/react.production.min.js
  • react-dom/dist/react-dom.js → react-dom/umd/react-dom.development.js
  • react-dom/dist/react-dom.min.js → react-dom/umd/react-dom.production.min.js

• The server renderer has been completely rewritten, with some improvements:
  • Server rendering does not use markup validation anymore, and instead tries its best to attach to existing DOM, warning about inconsistencies. It also doesn't use comments for empty components and data-reactid attributes on each node anymore.
  • Hydrating a server rendered container now has an explicit API. Use ReactDOM.hydrate instead of ReactDOM.render if you're reviving server rendered HTML. Keep using ReactDOM.render if you're just doing client-side rendering.
• When "unknown" props are passed to DOM components, for valid values, React will now render them in the DOM. See this post for more details. (@nhunzaker in #10385, 10564, #10495 and others)
• Errors in the render and lifecycle methods now unmount the component tree by default. To prevent this, add error boundaries to the appropriate places in the UI.

Removed Deprecations

• There is no react-with-addons.js build anymore. All compatible addons are published separately on npm, and have single-file browser versions if you need them.
• The deprecations introduced in 15.x have been removed from the core package. React.createClass is now available as create-react-class, React.PropTypes as prop-types, React.DOM as react-dom-factories, react-addons-test-utils as react-dom/test-utils, and shallow renderer as react-test-renderer/shallow. See 15.5.0 and 15.6.0 blog posts for instructions on migrating code and automated codemods.