@cypress/react

Test React components using Cypress

Usage no npm install needed!

<script type="module">
  import cypressReact from 'https://cdn.skypack.dev/@cypress/react';
</script>

README

A little helper to unit test React components in the open source Cypress.io test runner v7.0.0+

Jump to: Comparison, Blog posts, Install, Examples: basic, advanced, full, external, Style options, Code coverage, Visual testing, Common problems, Chat

TLDR

  • What is this? This package allows you to use Cypress test runner to unit test your React components with zero effort. Here is a typical component testing, notice there is not external URL shown, since it is mounting the component directly.

Example component test

Comparison

Feature Jest / Enzyme / RTL Cypress + @cypress/react
Test runs in real browser
Supports shallow mount
Supports full mount
Test speed 🏎 as fast as the app works in the browser
Test can use additional plugins maybe use any Cypress plugin
Test can interact with component synthetic limited API use any Cypress command
Test can be debugged via terminal and Node debugger use browser DevTools
Built-in time traveling debugger Cypress time traveling debugger
Re-run tests on file or test change
Test output on CI terminal terminal, screenshots, videos
Tests can be run in parallel ✅ via parallelization
Test against interface if using @testing-library/react ✅ and can use @testing-library/cypress
Spying and stubbing methods Jest mocks Sinon library
Stubbing imports
Stubbing clock
Code coverage

If you are coming from Jest + RTL world, read Test The Interface Not The Implementation.

If you are coming from Enzyme world, check out the enzyme example.

Blog posts

Install

Requires Node version 12 or above.

npm install --save-dev cypress @cypress/react @cypress/webpack-dev-server

Init

You can use our command line wizard to give you instructions on configuring this plugin. It will try to determine which framework or bundling tool you are using and give you instructions on right configuration.

npx create-cypress-tests --component-tests

Or continue with manual installation in the plugin file

  1. Tell Cypress how your React application is transpiled or bundled (using Webpack), so Cypress can load your components. For example, if you use react-scripts (even after ejecting) do:
// cypress/plugins/index.js
module.exports = (on, config) => {
  require('@cypress/react/plugins/react-scripts')(on, config)
  // IMPORTANT to return the config object
  // with the any changed environment variables
  return config
}

See Recipes for more examples.

  1. You can specify where component spec files are located. For example, to have them located in src folder use:
{
  "componentFolder": "src"
}

API

  • mount is the most important function, allows to mount a given React component as a mini web application and interact with it using Cypress commands
  • createMount factory function that creates new mount function with default options
  • unmount removes previously mounted component, mostly useful to test how the component cleans up after itself
  • mountHook mounts a given React Hook in a test component for full testing, see hooks example

Examples

import React from 'react'
import { mount } from '@cypress/react'
import { HelloWorld } from './hello-world.jsx'
describe('HelloWorld component', () => {
  it('works', () => {
    mount(<HelloWorld />)
    // now use standard Cypress commands
    cy.contains('Hello World!').should('be.visible')
  })
})

Look at the examples in cypress/component folder. Here is the list of examples showing various testing scenarios.

Basic examples

Spec Description
alias Retrieve mounted component by its name or alias
alert-spec.js Component tries to use window.alert
before-hook Mount the component from before hook to run multiple tests against it
counter-set-state Counter component that uses this.state
counter-use-hooks Counter component that uses useState hook
document-spec Checks document dimensions from the component
enzyme Several specs showing how to recreate Enzyme's setProps, setState, and setContext methods.
emotion-spec.js Confirms the component is using @emotion/core and styles are set
error-boundary-spec.js Checks if an error boundary component works
fails-correctly Cypress test fails correctly when interacting with disabled elements
pure-component-spec.js Tests stateless component
stateless-spec.js Passes Cypress stub to the component, confirms the component calls it on click
window-spec.js In the component test, the spec window and the application's window where the component is running should be the same object
css Shows that component with import './Button.css' works
css modules Shows that component that using css modules styles works
network Confirms we can use cy.route to stub / spy on component's network calls
no-visit Component specs cannot call cy.visit
re-render Checking how the component re-renders when its props change
react-book-by-chris-noring Copied test examples from React Book and adapted for Cypress component tests
react-tutorial Tests from official ReactJS tutorial copied and adapted for Cypress component tests
stub-example Uses cy.stub as component props
styles Add extra styles to the component during testing using style, cssFile or stylesheets mount options
toggle-example Testing a toggle component using Cypress DOM commands
typescript A spec written in TypeScript
unmount Verifies the component's behavior when it is unmounted from the DOM
use-lodash-fp Imports and tests methods from lodash/fp dependency
styled-components Test components that use styled-components

plus a few smaller sanity specs in cypress/component/basic folder.

Advanced examples

Spec Description
api-test Mix REST api tests that use cy-api with component tests
app-action-example App actions against components
context Confirms components that use React context feature work
custom-command Wraps mount in a custom command for convenience
forward-ref Tests a component that uses a forward ref feature
hooks Tests several components that use React Hooks like useState, useCallback
lazy-loaded Confirms components that use React.lazy and dynamic imports work
material-ui-example Large components demos from Material UI
mobx-v6 Test components with MobX v6 observable
mock-fetch Test stubs window.fetch used by component in useEffect hook
mocking-axios Stubbing methods from a 3rd party component like axios
mocking-component Replaced a child component with dummy component during test
mocking-imports Stub a named ES6 import in various situations
react-router-v6 Example testing a React Router v6. Both browser and in memory routers
renderless Testing a component that does not need to render itself into the DOM
set-timeout-example Control the clock with cy.tick and test loading components that use setTimeout
test-retries This component is compatible with Cypress Test Retries
testing-lib-example A spec adopted from @testing-library/react that uses @testing-library/cypress
timers Testing components that set timers, adopted from ReactJS Testing recipes
tutorial A few tests adopted from ReactJS Tutorial, including Tic-Tac-Toe game
use-local-storage Use hooks to load and save items into localStorage
portal Component test for ReactDOM.createPortal feature
radioactive-state Testing components that use radioactive-state library
react-bootstrap Confirms react-bootstrap components are working
select React component Uses cypress-react-selector to find DOM elements using React component name and state values
lazy-loaded Uses multiple chunks and async components with React.lazy + React.Suspense.
i18n Usesreact-i18next for localizaiton.
framer-motion Uses framer motion for javascript-based animation.

Full examples

We have several subfolders in examples folder that have complete projects with just their dependencies installed in the root folder.

Folder Name Description
a11y Testing components' accessibility using cypress-axe
react-scripts A project using react-scripts with component tests in src folder, including the .env files demo.
react-scripts-folder A project using react-scripts with component tests in cypress/component
tailwind Testing styles built using Tailwind CSS
sass-and-ts Example with Webpack, Sass and TypeScript
snapshots Component HTML and JSON snapshots using cypress-plugin-snapshots
visual-sudoku Visual testing for components using open source plugin cypress-image-snapshot. For larger example with an hour long list of explanation videos, see bahmutov/sudoku.
visual-testing-with-percy Visual testing for components using 3rd party service Percy.io
visual-testing-with-happo Visual testing for components using 3rd party service Happo
visual-testing-with-applitools Visual testing for components using 3rd party service Applitools.com
using-babel Bundling specs and loaded source files using project's existing .babelrc file
webpack-file Bundle component and specs using rollup.
webpack-file Load existing webpack.config.js file
webpack-options Using the default Webpack options from @cypress/webpack-preprocessor to transpile JSX specs

External examples

This way of component testing has been verified in a number of forked 3rd party projects.

Repo Description
try-cra-with-unit-test Hello world initialized with CRAv3
try-cra-app-typescript Hello world initialized with CRAv3 --typescript
react-todo-with-hooks Modern web application using hooks
test-redux-examples Example apps copies from official Redux repo and tested as components
test-react-hooks-animations Testing React springs fun blob animation
test-mdx-example Example testing MDX components using Cypress
test-apollo Component testing an application that uses Apollo GraphQL library
test-xstate-react XState component testing using Cypress
test-react-router-v5 A few tests of React Router v5
test-material-ui Testing Material UI components: date pickers, lists, autocomplete
test-d3-react-gauge Testing React D3 gauges
storybook-code-coverage Example app where we get 100% code coverage easily with a single integration spec and a few component specs, replacing several tools
react-loading-skeleton One to one Storybook tests for React skeleton components. Uses local .babelrc settings without Webpack config
test-swr Component test for Zeit SWR hooks for remote data fetching
emoji-search Quick component test for a fork of emoji-search
test-custom-error-boundary Play with a component that implements error boundary
Jscrambler-Webpack-React Example project with its own Webpack config file
bahmutov/integration-tests Example based on blog post React Integration Testing: Greater Coverage, Fewer Tests
mobx-react-typescript-boilerplate Fork of the official Mobx example, shows clock control
bahmutov/test-react-hook-form Testing forms created using react-hook-form
bahmutov/react-with-rollup Testing a React application bundled with Rollup by using @bahmutov/cy-rollup preprocessor
bahmutov/testing-react-example Described in blog post Test React Component with @cypress/react Example
ejected-react-scripts-example Using component testing after ejecting react-scripts
tic-tac-toe Component and unit tests for Tic-Tac-Toe, read Tic-Tac-Toe Component Tests
react-hooks-file-upload Upload a file from the component while stubbing the server
react-query-example Quick test example for components that use react-query with mock clock control

To find more examples, see GitHub topic @cypress/react-example

Options

In most cases, the component already imports its own styles, thus it looks "right" during the test. If you need another CSS, the simplest way is to import it from the spec file:

// src/Footer.spec.js
import './styles/main.css'
import Footer from './Footer'
it('looks right', () => {
  // styles are applied
  mount(<Footer />)
})

Extra styles

You can pass additional styles, css files and external stylesheets to load, see docs/styles.md for the full list of options.

const todo = {
  id: '123',
  title: 'Write more tests',
}
mount(<Todo todo={todo} />, {
  stylesheets: [
    'https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.css',
  ],
})
Additional configuration If your React and React DOM libraries are installed in non-standard paths (think monorepo scenario), you can tell this plugin where to find them. In `cypress.json` specify paths like this:
{
  "env": {
    "@cypress/react": {
      "react": "node_modules/react/umd/react.development.js",
      "react-dom": "node_modules/react-dom/umd/react-dom.development.js"
    }
  }
}

You may also specify the ReactDOM package to use. This can be useful in complex monorepo setups that have different versions of React and React DOM installed. If you see an error relating to mismatching versions of React or React DOM, this may be the solution. You can do this using the ReactDom option:

// if you have multiple versions of ReactDom in your monorepo
import ReactDom from 'react-dom'

mount(<Todo todo={todo} />, {
  stylesheets: [
    'https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.css',
  ],
  ReactDom
})

Code coverage

In order to use code coverage you can follow the instructions from docs. In most of cases you need to install 2 dependencies:

npm i @cypress/code-coverage babel-plugin-istanbul

yarn add @cypress/code-coverage babel-plugin-istanbul

If you are using plugins/cra-v3 it instruments the code on the fly using babel-plugin-istanbul and generates report using dependency cypress-io/code-coverage (included). If you want to disable code coverage instrumentation and reporting, use --env coverage=false or CYPRESS_coverage=false or set in your cypress.json file

{
  "env": {
    "coverage": false
  }
}

Visual testing

You can use any Cypress Visual Testing plugin to perform visual testing from the component tests. This repo has several example projects, see visual-sudoku, visual-testing-with-percy, visual-testing-with-happo, and visual-testing-with-applitools.

For a larger Do-It-Yourself example with an hour long list of explanation videos, see bahmutov/sudoku repository. I explain how to write visual testing using open source tools in this blog post, video talk, and slides.

Common problems

Slower than Jest

When you use cypress-X-unit-test for component testing, you might notice the tests are slower than using Jest to test the same components. Yes, that's true. A test runner could be made extremely fast if it did nothing, just check out the auchenberg/volkswagen test runner - it is blazing on CI 😉. Of course, Jest does do things, just not inside the real browser environment.

Testing using Jest with its jsdom browser is faster than starting the real browser, loading all libraries, mounting the component and then waiting for the component to actually perform its work in response to the test's actions. But do those tests give you a true confidence that the component is working?

Try this test 🙈

Spoiler: it fails, proof.

const mock = jest.fn()
// render a component that does NOT allow any click events
// using pointerEvents: "none" style
const { getByRole } = render(
  <button style={{ pointerEvents: 'none' }} onClick={mock}>
    text
  </button>,
)
// Jest happily clicks
fireEvent.click(getByRole('button'))
expect(mock).not.toBeCalled()

Cypress test on the other hand fails correctly.

We think that using cypress-X-unit-test runs tests as fast as your application code is, and often you need to think how to slow down the Cypress Test Runner so it does not run away from the component's code, just see our blog posts dealing with test flake.

From the developer's perspective I would ask myself: which tests do I write faster? What happens when a test fails and I need to debug the failure: which test runner allows me to debug a failed test quicker? While I am partial, I have to say, realistic Cypress tests are easier to write and debug.

Finally, when running tests on the continuous integration service, the true test speed up comes from properly configuring dependencies caching and running tests in parallel - something we have extensively documented and consider a solved problem.

Context Provider usage

React context provider usage and API described in ./docs/providers-and-composition.md

Chat

Come chat with us on discord in the #component-testing channel.

Development

See docs/development.md

Debugging

You can see verbose logs from this plugin by running with environment variable

DEBUG=@cypress/react

Because finding and modifying Webpack settings while running this plugin is done by find-webpack module, you might want to enable its debug messages too.

DEBUG=@cypress/react,find-webpack

Changelog

Changelog

Related tools

Same feature for unit testing components from other frameworks using Cypress