cypress-react-unit-test

cypress-react-unit-test

A little helper to unit test React components in the open source Cypress.io E2E test runner v4.5.0+

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

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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.

• How is this different from Enzyme or RTL? It is similar in functionality BUT runs the component in the real browser with full power of Cypress E2E test runner: live GUI, full API, screen recording, CI support, cross-platform, and visual testing. Ohh, and the code coverage is built-in!
• If you like using @testing-library/react, you can use @testing-library/cypress for the same findBy, queryBy commands, see one of the examples in the list below
• Read My Vision for Component Tests in Cypress

Comparison

Feature	Jest / Enzyme / RTL	Cypress + cypress-react-unit-test
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	✅	✅

Blog posts

• My Vision for Component Tests in Cypress
• Unit Testing React components with Cypress
• Test React Component with cypress-react-unit-test Example
• Tic-Tac-Toe Component Tests
• Using .env and .env.test from React component tests
• Visual testing for React components using open source tools
• 12 Recipes for testing React applications using cypress-react-unit-test (compare to 12 Recipes for testing React applications using Testing Library)

Known problems

See issues labeled v4

Install

Requires Node version 8 or above.

npm install --save-dev cypress cypress-react-unit-test

1. Include this plugin from your project's cypress/support/index.js

require('cypress-react-unit-test/support')

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-unit-test/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. ⚠️ Turn the experimental component support on in your cypress.json. You can also specify where component spec files are located. For example, to have them located in src folder use:

{
  "experimentalComponentTesting": true,
  "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
• 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-unit-test'
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
counter-set-state	Counter component that uses this.state
counter-use-hooks	Counter component that uses useState hook
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
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
network	Confirms we can use cy.route to stub / spy on component's network calls
no-visit	Component specs cannot call cy.visit
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
document-spec	Checks document dimensions from the component
styled-components	Test components that use styled-components

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

Advanced examples

Spec	Description
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
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 using plugin-transform-modules-commonjs with loose: true when transpiled
react-router-v6	Example testing a React Router v6
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
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
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

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	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-unit-test 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-unit-test-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-unit-test": {
      "react": "node_modules/react/umd/react.development.js",
      "react-dom": "node_modules/react-dom/umd/react-dom.development.js"
    }
  }
}

Code coverage

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

Node Sass

When using Node Sass styles, tell Cypress to use the system NodeJS rather than its bundled version. In cypress.json set option:

{
  "nodeVersion": "system"
}

Find full example in sass-and-ts folder.

Slow bundling

When you bundle spec file, you are now bundling React, Read DOM and other libraries, which is might be slow. For now, you can disable inline source maps by adding to your Webpack config settings (if available) the following:

const webpackOptions = {
  devtool: false,
}

Keep your eye on issue #156 for more information.

Missing code coverage

If you are using your custom Webpack, this plugin might be missing code coverage information because the code was not instrumented. We try to insert the babel-plugin-istanbul plugin automatically, but your bundling might not use Babel, or configure it differently, preventing plugin insertion. Please let us know by opening an issue with full reproducible details.

See related issue #141. You can also debug the plugin's behavior by running it with DEBUG environment variable, see #debugging section.

Next.js projects not supported

Currently, this project cannot find Webpack settings used by Next.js, thus it cannot bundle specs and application code correctly. Keep an eye on #155

Gatsby.js projects not supported

Currently, this project cannot find Webpack settings used by Gatsby.js, thus it cannot bundle specs and application code correctly. Keep an eye on #307

Development

See docs/development.md

Debugging

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

DEBUG=cypress-react-unit-test

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-unit-test,find-webpack

Migration guide

From v3 to v4

The old v3 main branch is available as branch v3

• the cy.mount is now simply import { mount } from 'cypress-react-unit-test'
• the support file is simply require('cypress-react-unit-test/support')

Related tools

Same feature for unit testing components from other frameworks using Cypress

• cypress-vue-unit-test
• cypress-cycle-unit-test
• cypress-svelte-unit-test
• cypress-angular-unit-test
• cypress-hyperapp-unit-test
• cypress-angularjs-unit-test