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jest-emotion
Advanced tools
Jest testing utilities for emotion
npm install --save-dev jest-emotion
The easiest way to test React components with emotion is with the snapshot serializer. You can register the serializer via the snapshotSerializers
configuration property in your jest configuration like so:
// jest.config.js
module.exports = {
// ... other config
snapshotSerializers: ['jest-emotion']
}
Or you can customize the serializer via the createSerializer
method like so: (the example below is with react-test-renderer but jest-emotion also works with enzyme and react-testing-library)
import React from 'react'
import renderer from 'react-test-renderer'
import serializer from 'jest-emotion'
import styled from '@emotion/styled'
expect.addSnapshotSerializer(serializer)
test('renders with correct styles', () => {
const H1 = styled.h1`
float: left;
`
const tree = renderer.create(<H1>hello world</H1>).toJSON()
expect(tree).toMatchSnapshot()
})
Refer to the testing doc for more information about snapshot testing with emotion.
classNameReplacer
jest-emotion's snapshot serializer replaces the hashes in class names with an index so that things like whitespace changes won't break snapshots. It optionally accepts a custom class name replacer, it defaults to the below.
function classNameReplacer(className, index) {
return `emotion-${index}`
}
import { createSerializer } from 'jest-emotion'
expect.addSnapshotSerializer(
createSerializer({
classNameReplacer(className, index) {
return `my-new-class-name-${index}`
}
})
)
DOMElements
jest-emotion's snapshot serializer inserts styles and replaces class names in both React and DOM elements. If you would like to disable this behavior for DOM elements, you can do so by passing { DOMElements: false }
. For example:
import { createSerializer } from 'jest-emotion'
// configures jest-emotion to ignore DOM elements
expect.addSnapshotSerializer(createSerializer({ DOMElements: false }))
To make more explicit assertions when testing your styled components you can use the toHaveStyleRule
matcher.
import React from 'react'
import renderer from 'react-test-renderer'
import { matchers } from 'jest-emotion'
import styled from '@emotion/styled'
// Add the custom matchers provided by 'jest-emotion'
expect.extend(matchers)
test('renders with correct styles', () => {
const Svg = styled('svg')`
width: 100%;
`
const Div = styled('div')`
float: left;
height: 80%;
&:hover {
width: 50px;
}
${Svg} {
fill: green;
}
span {
color: yellow;
}
@media screen and (max-width: 1200px) {
font-size: 14px;
}
`
const tree = renderer
.create(
<Div>
<Svg />
<span>Test</span>
</Div>
)
.toJSON()
expect(tree).toHaveStyleRule('float', 'left')
expect(tree).not.toHaveStyleRule('height', '100%')
})
You can provide additional options for toHaveStyleRule
matcher.
target
- helps to specify css selector or other component
where style rule should be found.
expect(tree).toHaveStyleRule('width', '50px', { target: ':hover' })
expect(tree).toHaveStyleRule('color', 'yellow', { target: 'span' })
expect(tree).toHaveStyleRule('fill', 'green', { target: `${Svg}` })
media
- specifies the media rule where the matcher
should look for the style property.
expect(tree).toHaveStyleRule('font-size', '14px', {
media: 'screen and (max-width: 1200px)'
})
Use media
and target
options to assert on rules within media queries and to target nested components, pseudo-classes, and pseudo-elements.
import React from 'react'
import renderer from 'react-test-renderer'
import { matchers } from 'jest-emotion'
import styled from '@emotion/styled'
// Add the custom matchers provided by 'jest-emotion'
expect.extend(matchers)
test('renders with correct link styles', () => {
const Container = styled.div`
font-size: 14px;
a {
color: yellow;
}
a:hover {
color: black;
}
@media (min-width: 768px) {
font-size: 16px;
}
`
const tree = renderer.create(<Container>hello world</Container>).toJSON()
expect(tree).toHaveStyleRule('color', 'yellow', { target: /a$/ })
expect(tree).toHaveStyleRule('color', 'black', { target: 'a:hover' })
expect(tree).toHaveStyleRule('font-size', '16px', {
media: '(min-width: 768px)'
})
})
Thanks to Kent C. Dodds who wrote jest-glamor-react which this library is largely based on. ❤️
FAQs
Jest utilities for emotion
The npm package jest-emotion receives a total of 28,015 weekly downloads. As such, jest-emotion popularity was classified as popular.
We found that jest-emotion demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 4 open source maintainers collaborating on the project.
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