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 ALPHA

TLDR

• What is this? This package allows you to use Cypress test runner to unit test your React components with zero effort.

• How is this different from Enzyme? 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.

Known problems

• some DOM events are not working when running all tests at once #4
• cannot mock server XHR for injected components #5
• cannot spy on window.alert #6

Install

Requires Node version 8 or above.

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

If you need help configuring bundler, see preprocessors info

Use

Include this plugin from cypress/support/index.js

import 'cypress-react-unit-test'

This adds a new command cy.mount that can mount a React component. It also overloads cy.get to accept in addition to selectors React component, returning it. See examples below.

Example

// load Cypress TypeScript definitions for IntelliSense
/// <reference types="cypress" />
// import the component you want to test
import { HelloState } from '../../src/hello-x.jsx'
import React from 'react'
describe('HelloState component', () => {
  it('works', () => {
    // mount the component under test
    cy.mount(<HelloState />)
    // start testing!
    cy.contains('Hello Spider-man!')
    // mounted component can be selected via its name, function, or JSX
    // e.g. '@HelloState', HelloState, or <HelloState />
    cy.get(HelloState)
      .invoke('setState', { name: 'React' })
    cy.get(HelloState)
      .its('state')
      .should('deep.equal', { name: 'React' })
    // check if GUI has rerendered
    cy.contains('Hello React!')
  })
})

styles

You can add individual style to the mounted component by passing its text as an option

it('can be passed as an option', () => {
  const style = `
    .component-button {
      display: inline-flex;
      width: 25%;
      flex: 1 0 auto;
    }

    .component-button.orange button {
      background-color: #F5923E;
      color: white;
    }
  `
  cy.mount(<Button name='Orange' orange />, null, { style })
  cy.get('.orange button')
    .should('have.css', 'background-color', 'rgb(245, 146, 62)')
})

Often your component rely on global CSS style imported from the root index.js or app.js file

// index.js
import './styles.css'
// bootstrap application

You can read the CSS file and pass it as style option yourself

cy.readFile('cypress/integration/Button.css')
  .then(style => {
    cy.mount(<Button name='Orange' orange />, null, { style })
  })

You can even let Cypress read the file and inject the style

const cssFile = 'cypress/integration/Button.css'
cy.mount(<Button name='Orange' orange />, null, { cssFile })

See cypress/integration/inject-style-spec.js for more examples.

re-render

Sometimes you need to re-render the component, for example when a Redux store changes. After cy.mount completes (asynchronously), you can call cy.render(JSXElement) method.

cy.mount(<El text='first' />)
cy.contains('first')
  .then(() => {
    cy.render(<El text='second' />)
  })

See bahmutov/redux-counter-example example spec file src/App.cy-spec.js.

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"
    }
  }
}

Transpilation

How can we use features that require transpilation? By using @cypress/webpack-preprocessor - see the plugin configuration in cypress/plugins/index.js

Create React App users

If you are using Create-React-App v3, and want to reuse the built in webpack before ejecting, this module ships with Cypress preprocessor in plugins folder. From the cypress.json point at the shipped plugin in the node_modules.

{
  "pluginsFile": "node_modules/cypress-react-unit-test/plugins/cra-v3",
  "supportFile": "node_modules/cypress-react-unit-test/support"
}

See example repo bahmutov/try-cra-with-unit-test

If you already have a plugins file, you can use a file preprocessor that points at CRA's webpack

// your project's Cypress plugin file
const craFilePreprocessor = require('cypress-react-unit-test/plugins/cra-v3/file-preprocessor')
module.exports = on => {
  on('file:preprocessor', craFilePreprocessor())
}

Examples

All components are in src folder. All tests are in cypress/integration folder.

• hello-world-spec.js - testing the simplest React component from hello-world.jsx
• hello-x-spec.js - testing React component with props and state hello-x.jsx
• counter-spec.js clicks on the component and confirms the result
• stateless-spec.js shows testing a stateless component from stateless.jsx
• transpiled-spec.js shows testing a component with class properties syntax from transpiled.jsx
• error-boundary-spec.js shows testing a component acting as an error boundary from error-boundary.jsx
• users-spec.js shows how to observe XHR requests, mock server responses for component users.jsx
• alert-spec.js shows how to spy on window.alert calls from your component stateless-alert.jsx

Large examples

• bahmutov/calculator tests multiple components: calculator App, Button, Display.

Development

To get started with this repo, compile the plugin's code and the examples code

npm run transpile
npm run build
npm run cy:open

• run TypeScript compiler in watch mode with npx tsc -w
• run Cypress with npx cypress open and select the spec you want to work with
• edit lib/index.ts where all the magic happens

Visual testing

Uses Percy.io visual diffing service as a GitHub pull request check.

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