jest-axe

Custom Jest matcher for aXe for testing accessibility

⚠️✋ This project does not guarantee what you build is accessible.

The GDS Accessibility team found that only ~30% of issues are found by automated testing.

Tools like aXe are similar to code linters such as eslint or sass-lint: they can find common issues but cannot guarantee what you build works for users.

You'll also need to:

• test your interface with the assistive technologies that real users use (see also WebAIM's survey results).
• include people with disabilities in user research.

Installation:

npm install --save-dev jest-axe

Usage:

const { axe, toHaveNoViolations } = require('jest-axe')

expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage', async () => {
  const render = () => '<img src="#"/>'

  // pass anything that outputs html to axe
  const html = render()

  expect(await axe(html)).toHaveNoViolations()
})

Note, you can also require 'jest-axe/extend-expect' which will call expect.extend for you. This is especially helpful when using the jest setupTestFrameworkScriptFile configuration.

Testing React

const React = require('react')
const { render } =  require('react-dom')
const App = require('./app')

const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with react', async () => {
  render(<App/>, document.body)
  const results = await axe(document.body)
  expect(results).toHaveNoViolations()
})

Testing React with Enzyme

const React = require('react')
const App = require('./app')

const { mount } = require('enzyme')
const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with enzyme', async () => {
  const wrapper = mount(<App/>)
  const results = await axe(container.getDOMNode())
  
  expect(results).toHaveNoViolations()
})

Testing React with React Testing Library

const React = require('react')
const App = require('./app')

const { render, cleanup } = require('@testing-library/react')
const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with react testing library', async () => {
  const { container } = render(<App/>)
  const results = await axe(container)
  
  expect(results).toHaveNoViolations()
  
  cleanup()
})

Note: If you're using react testing library you should be using the cleanup method. This method removes the rendered application from the DOM and ensures a clean HTML Document for further testing.

Testing Vue with Vue Test Utils

const App = require('./App.vue')

const { mount } = require('@vue/test-utils')
const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with vue test utils', async () => {
  const wrapper = mount(Image)
  const results = await axe(wrapper.element)

  expect(results).toHaveNoViolations()
})

Testing Vue with Vue Testing Library

const React = require('react')
const App = require('./app')

const { render, cleanup } = require('@testing-library/vue')
const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with react testing library', async () => {
  const { container } = render(<App/>)
  const results = await axe(container)
  
  expect(results).toHaveNoViolations()
  
  cleanup()
})

Note: If you're using vue testing library you should be using the cleanup method. This method removes the rendered application from the DOM and ensures a clean HTML Document for further testing.

Axe configuration

The axe function allows options to be set with the same options as documented in axe-core:

const { axe, toHaveNoViolations } = require('jest-axe')

expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with a custom config', async () => {
  const render = () => `
    <div>
      <img src="#"/>
    </div>
  `

  // pass anything that outputs html to axe
  const html = render()

  const results = await axe(html, {
    rules: {
      // for demonstration only, don't disable rules that need fixing.
      'image-alt': { enabled: false }
    }
  })

  expect(results).toHaveNoViolations()
})

Setting global configuration

If you find yourself repeating the same options multiple times, you can export a version of the axe function with defaults set.

Note: You can still pass additional options to this new instance; they will be merged with the defaults.

This could be done in Jest's setup step

// Global helper file (axe-helper.js)
const { configureAxe } = require('jest-axe')

const axe = configureAxe({
  rules: {
    // for demonstration only, don't disable rules that need fixing.
    'image-alt': { enabled: false }
  }
})

module.exports = axe

// Individual test file (test.js)
const { toHaveNoViolations } = require('jest-axe')
const axe = require('./axe-helper.js')

expect.extend(toHaveNoViolations)

it('should demonstrate this matcher`s usage with a default config', async () => {
  const render = () => `
    <div>
      <img src="#"/>
    </div>
  `

  // pass anything that outputs html to axe
  const html = render()

  expect(await axe(html)).toHaveNoViolations()
})

Thanks

• Jest for the great test runner that allows extending matchers.
• aXe for the wonderful axe-core that makes it so easy to do this.
• Government Digital Service for making coding in the open the default.
  • GOV.UK Publishing Frontend team who published the basis of the aXe reporter
• jest-image-snapshot for inspiration on README and repo setup