You want to use jest to write tests that assert various things about the state of a DOM. As part of that goal, you want to avoid all the repetitive patterns that arise in doing so. Checking for an element's attributes, its text content, its css classes, you name it.
The jest-dom library provides a set of custom jest matchers that you can use
to extend jest. These will make your tests more declarative, clear to read and
to maintain.
- Installation
- Usage
- Custom matchers
- Inspiration
- Other Solutions
- Guiding Principles
- Contributors
- LICENSE
This module is distributed via npm which is bundled with node and
should be installed as one of your project's devDependencies:
npm install --save-dev jest-dom
Import jest-dom/extend-expect once (for instance in your tests setup file)
and you're good to go:
import 'jest-dom/extend-expect'Alternatively, you can selectively import only the matchers you intend to use,
and extend jest's expect yourself:
import {toBeInTheDOM, toHaveClass} from 'jest-dom'
expect.extend({toBeInTheDOM, toHaveClass})Note: when using TypeScript, this way of importing matchers won't provide the necessary type definitions. More on this here.
This allows you to assert whether an element present in the DOM or not.
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <span data-testid="count-value">2</span>
expect(queryByTestId(container, 'count-value')).toBeInTheDOM()
expect(queryByTestId(container, 'count-value1')).not.toBeInTheDOM()
// ...Note: when using
toBeInTheDOM, make sure you use a query function (likequeryByTestId) rather than a get function (likegetByTestId). Otherwise theget*function could throw an error before your assertion.
This API allows you to check whether the given element has a text content or not.
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <span data-testid="count-value">2</span>
expect(getByTestId(container, 'count-value')).toHaveTextContent('2')
expect(getByTestId(container, 'count-value')).not.toHaveTextContent('21')
// ...This allows you to check wether the given element has an attribute or not. You can also optionally check that the attribute has a specific expected value.
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <button data-testid="ok-button" type="submit" disabled>
// OK
// </button>
expect(getByTestId(container, 'ok-button')).toHaveAttribute('disabled')
expect(getByTestId(container, 'ok-button')).toHaveAttribute('type', 'submit')
expect(getByTestId(container, 'ok-button')).not.toHaveAttribute(
'type',
'button',
)
// ...This allows you to check wether the given element has certain classes within its
class attribute.
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <button data-testid="delete-button" class="btn extra btn-danger">
// Delete item
// </button>
expect(getByTestId(container, 'delete-button')).toHaveClass('extra')
expect(getByTestId(container, 'delete-button')).toHaveClass('btn-danger btn')
expect(getByTestId(container, 'delete-button')).not.toHaveClass('btn-link')
// ...This allows you to check if a certain element has some specific css properties with specific values applied. It matches only if the element has all the expected properties applied, not just some of them.
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <button data-testid="delete-button" style="display: none; color: red">
// Delete item
// </button>
expect(getByTestId(container, 'delete-button')).toHaveStyle('display: none')
expect(getByTestId(container, 'delete-button')).toHaveStyle(`
color: red;
display: none;
`)
expect(getByTestId(container, 'delete-button')).not.toHaveStyle(`
display: none;
color: blue;
`)
// ...This also works with rules that are applied to the element via a class name for which some rules are defined in a stylesheet currently active in the document. The usual rules of css precedence apply.
This allows you to check if an element is currently visible to the user.
An element is visible if all the following conditions are met:
- it does not have its css property
displayset tonone - it does not have its css property
visibilityset to eitherhiddenorcollapse - it does not have its css property
opacityset to0 - its parent element is also visible (and so on up to the top of the DOM tree)
// add the custom expect matchers once
import 'jest-dom/extend-expect'
// ...
// <header>
// <h1 style="display: none">Page title</h1>
// </header>
// <section>
// <p style="visibility: hidden">Hello <strong>World</strong></h1>
// </section>
expect(container.querySelector('header')).toBeVisible()
expect(container.querySelector('h1')).not.toBeVisible()
expect(container.querySelector('strong')).not.toBeVisible()
// ...This whole library was extracted out of Kent C. Dodds' dom-testing-library, which was in turn extracted out of react-testing-library.
The intention is to make this available to be used independently of these other libraries, and also to make it more clear that these other libraries are independent from jest, and can be used with other tests runners as well.
I'm not aware of any, if you are please make a pull request and add it here!
The more your tests resemble the way your software is used, the more confidence they can give you.
This library follows the same guiding principles as its mother library dom-testing-library. Go check them out for more details.
Additionally, with respect to custom DOM matchers, this library aims to maintain a minimal but useful set of them, while avoiding bloating itself with merely convenient ones that can be easily achieved with other APIs. In general, the overall criteria for what is considered a useful custom matcher to add to this library, is that doing the equivalent assertion on our own makes the test code more verbose, less clear in its intent, and/or harder to read.
Thanks goes to these people (emoji key):
This project follows the all-contributors specification. Contributions of any kind welcome!
MIT