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 />, { 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 />, { 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 />, { 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 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

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
  }
}

Create React App users

If you are using Create-React-App v3 or react-scripts, 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())
}

Bonus: re-using the config means if you create your application using create-react-app --typescript, then TypeScript transpile just works out of the box. See bahmutov/try-cra-app-typescript.

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/test-redux-examples has bunch of official Redux app examples with equivalent Cypress unit tests
• 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