jest-axe
Custom Jest matcher for axe for testing accessibility
⚠️✋ This project does not guarantee that 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 stylelint: they can find common issues but cannot guarantee that what you build works for users.
You'll also need to:
Checks that do not work in jest-axe
Color contrast checks do not work in JSDOM so are turned off in jest-axe.
Installation:
npm install --save-dev jest jest-axe jest-environment-jsdom
TypeScript users can install the community maintained types package:
npm install --save-dev @types/jest-axe
Usage:
const { axe, toHaveNoViolations } = require('jest-axe')
expect.extend(toHaveNoViolations)
it('should demonstrate this matcher`s usage', async () => {
const render = () => '<img src="#"/>'
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 setupFilesAfterEnv
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()
})
const React = require('react')
const App = require('./app')
const { render } = 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()
})
Note: If you're using react testing library
<9.0.0 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.
If you're using React Portals, use the baseElement
instead of container
:
it('should work with React Portals as well', async () => {
const { baseElement } = render(<App/>)
const results = await axe(baseElement)
expect(results).toHaveNoViolations()
})
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()
})
const App = require('./app')
const { render } = 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()
})
Note: If you're using vue testing library
<3.0.0 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 Angular with Nx
import { ComponentFixture, TestBed } from "@angular/core/testing";
import { axe } from "jest-axe";
import { SomeComponent } from "./some.component";
describe("SomeComponent", () => {
let fixture: ComponentFixture<SomeComponent>;
beforeEach(() => {
TestBed.configureTestingModule({
declarations: [SomeComponent],
});
fixture = TestBed.createComponent(SomeComponent);
});
it("should create", async () => {
const results = await axe(fixture.nativeElement);
expect(results).toHaveNoViolations();
});
});
Note: You may need to extend jest by importing jest-axe/extend-expect
at test-setup.ts
Usage with jest.useFakeTimers() or mocking setTimeout
thrown: "Exceeded timeout of 5000 ms for a test.
Use jest.setTimeout(newTimeout) to increase the timeout value, if this is a long-running test."
aXe core does not work when timers (setTimeout) are mocked. When using jest.useFakeTimers()
aXe core will timeout often causing failing tests.
We recommend renabling the timers temporarily for aXe:
jest.useRealTimers();
const results = await axe(wrapper.element);
jest.useFakeTimers();
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>
`
const html = render()
const results = await axe(html, {
rules: {
'image-alt': { enabled: false }
}
})
expect(results).toHaveNoViolations()
})
Testing isolated components
All page content must be contained by landmarks (region)
When testing with aXe sometimes it assumes you are testing a page. This then results in unexpected violations for landmarks for testing isolation components.
You can disable this behaviour with the region
rule:
const { configureAxe } = require('jest-axe')
const axe = configureAxe({
rules: {
'region': { enabled: false }
}
})
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
const { configureAxe } = require('jest-axe')
const axe = configureAxe({
rules: {
'image-alt': { enabled: false }
}
})
module.exports = axe
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>
`
const html = render()
expect(await axe(html)).toHaveNoViolations()
})
Setting custom rules and checks.
The configuration object passed to configureAxe
, accepts a globalOptions
property to configure the format of the data used by axe and to add custom checks and rules. The property value is the same as the parameter passed to axe.configure.
const { configureAxe } = require('jest-axe')
const axe = configureAxe({
globalOptions: {
checks: []
},
})
module.exports = axe
Setting the level of user impact.
An array which defines which impact level should be considered. This ensures that only violations with a specific impact on the user are considered. The level of impact can be "minor", "moderate", "serious", or "critical".
const { configureAxe } = require('jest-axe')
const axe = configureAxe({
impactLevels: ['critical'],
})
module.exports = axe
Refer to Developing Axe-core Rules for instructions on how to develop custom rules and checks.
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.
- jest-image-snapshot for inspiration on README and repo setup