Migrate from Enzyme

This page does not go into detail, but it's for those who have experience in working with Enzyme and are trying to understand how to move to React Testing Library. It also has some helpful information for those who are comparing Enzyme with React Testing Library.

What is React Testing Library?

React Testing Library is part of an open-source project named Testing Library. There are several other helpful tools and libraries in the Testing Library project which you can use to write more useful tests. Besides React Testing Library, here are some other Testing Library's libraries that can help you along the way:

  • @testing-library/jest-dom: jest-dom 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.

  • @testing-library/user-event: user-event tries to simulate the real events that would happen in the browser as the user interacts with it. For example, userEvent.click(checkbox) would change the state of the checkbox.

Why should I use the React Testing Library?

Enzyme is a good test library. The library and its contributors did so much for the community. Many of the React Testing Library maintainers used and contributed to Enzyme for years before developing and working on React Testing Library. So we want to say, thank you to the contributors of Enzyme!

The primary purpose of the React Testing Library is to give you confidence by testing your components in the way the user will use them. Users don't care what happens behind the scenes. They just see and interact with the output. So, instead of accessing the components' internal API, or evaluating the state, you'll get more confidence by writing your tests based on the component output.

React Testing Library aims to solve the problem that many developers face when writing tests with Enzyme which allows (and encourages) developers to test implementation details. Tests which do this ultimately prevent you from modifying and refactoring the component without changing the test. As a result, the tests slowed down your development speed and productivity, since every small change requires rewriting some part of your tests, even if the change you made does not affect the component's output.

Re-writing your tests in React Testing library is worthwhile, because you're trading tests that slow you down for tests that give you more confidence and increase your productivity in the long run.

How to migrate from Enzyme to React Testing Library?

One of the keys to a successful migration is to do it incrementally, by running the two test libraries side by side in the same application and porting Enzyme's tests to React Testing Library one by one. It makes it possible to migrate even large and complex applications without disrupting other businesses because the work can be done collaboratively and spread over some time.

Install React Testing Library

You can check this page for the complete installation and setup guide.

Here is what you should do, first you need to install the React Testing Library:

npm install --save-dev @testing-library/react @testing-library/jest-dom

Import React Testing Library to your test

Let's say we're using Jest (you can use other test frameworks as well), then you just have to import the following modules into your test file:

// import React so you can use JSX (React.createElement) in your test
import React from 'react'
/**
* render: lets us render the component (like how React would)
* screen: Your utility for finding elements the same way the user does
**/
import {render, screen} from '@testing-library/react'

The test structure is as same as how you would write it in Enzyme

test('test title', () => {
// Your tests come here...
})

Note: you can also use describe and it blocks with React Testing Library. React Testing Library doesn't replace Jest, just Enzyme. We recommend test because it helps with this: Avoid Nesting When You're Testing

Basic Enzyme to React Testing Library migration examples

One thing to keep in mind that there's not a one-to-one mapping of Enzyme features to React Testing Library features. Many Enzyme features result in inefficient tests. Unfortunately, that means many of the features you're accustomed to with Enzyme will need to be left behind with Enzyme (no more need for a wrapper variable or wrapper.update() calls, etc.).

React Testing Library has helpful queries which lets you access your component's elements and their properties, and here we'll show typical Enzyme tests with React Testing Library's alternatives.

Let's say we have a Welcome component, which just shows a welcome message, and we will have a look at both Enzyme and React Testing Library tests to learn how we can test this component:

React Component

The following component gets a name from props and shows a welcome message in an h1 element, it also has a text input which users can change to a different name, and the template updates accordingly. Check the live version on Codesandbox

const Welcome = props => {
const [values, setValues] = useState({
firstName: props.firstName,
lastName: props.lastName,
})
const handleChange = event => {
setValues({...values, [event.target.name]: event.target.value})
}
return (
<div>
<h1>
Welcome, {values.firstName} {values.lastName}
</h1>
<form name="userName">
<label>
First Name
<input
value={values.firstName}
name="firstName"
onChange={handleChange}
/>
</label>
<label>
Last Name
<input
value={values.lastName}
name="lastName"
onChange={handleChange}
/>
</label>
</form>
</div>
)
}
export default Welcome

Test 1: Render the component, and check if the h1 value is correct

Enzyme test

test('has correct welcome text', () => {
const wrapper = shallow(<Welcome firstName="John" lastName="Doe" />)
expect(wrapper.find('h1').text()).to.equal('Welcome, John Doe')
})

React Testing library

test('has correct welcome text', () => {
render(<Welcome firstName="John" lastName="Doe" />)
expect(screen.getByRole('heading')).toHaveTextContent('Welcome, John Doe')
})

As you see, both are pretty similar, Enzyme's shallow wrapping doesn't descend down to sub-components, React Testing Library's render is more similar to mount.

In React Testing Library, you don't need to assign the render result to a variable (wrapper, or etc), and you can simply access the rendered output by calling the screen. The other good thing to know is that React Testing Library automatically cleans up the output for each test, so you don't need to call cleanup on Jest's afterEach or beforeEach function.

The other thing that you might notice is getByRole which has heading as its value. heading is the accessible role of the h1 element. You can learn more about them on queries documentation page. One of the things people quickly learn to love about Testing Library is how it encourages you to write more accessible applications (because if it's not accessible, then it's harder to test).

Test 2: Input texts must have correct value

In the component above, the input text value will be initialized with the props.firstName and props.lastName values, and we need to check whether the value is correct or not

Enzyme

test('has correct input value', () => {
const wrapper = shallow(<Welcome firstName="John" lastName="Doe" />)
expect(wrapper.find('input[name="firstName"]').value).to.equal('John')
expect(wrapper.find('input[name="lastName"]').value).to.equal('Doe')
})

React Testing Library

test('has correct input value', () => {
render(<Welcome firstName="John" lastName="Doe" />)
expect(screen.getByRole('form')).toHaveFormValues({
firstName: 'John',
lastName: 'Doe',
})
})

Cool! It's pretty simple and handy, and the tests are clear enough that we don't need to talk so much about them. But something that you might notice is that the <form> had a role="form" attribute, but what is it?

role is one of the accessibility-related attributes that is recommended to use to improve your web application for people with disabilities. Some elements have default role values and you don't need to set one for them, but some others like <div> do not have one. You could use different approaches to access the <div> element, but we recommend trying to access elements by their implicit role to make sure your component is accessible by people with disabilities and those who are using screen readers. This section of the query page might help you to understand better.

Keep in mind that a <form> must have a name attribute in order to have an implicit role of form (as required by the specification).

React Testing Library aims to test the component, like how users would, users see the button, heading, form and other elements by their role, not by their id or class, or element tag name. When you use React Testing Library, you should not try to access the DOM like how you would do by document.querySelector API (which you can incidentally use in your tests, but it's not recommended for the reasons stated in this paragraph).

We made some handy query APIs which help you to access the component elements very efficiently, and you can see the list of available queries in detail.

Something else that people have a problem with is that they're not sure which query should they use, luckily we have a great page which explains which query to use, so don't forget to check it out!

If you still have a problem with the React Testing Library's queries, and you're not sure which query to use, then check out testing-playground.com and the accompanying Chrome extension Testing Playground
that aims to enable developers to find a better query when writing tests, and it helps you find the best queries to select elements. It allows you to inspect the element hierarchies in the Chrome Developer Tools, and provides you with suggestions on how to select them, while encouraging good testing practices.

using act() and wrapper.update()

In Enzyme, for some asynchronous purposes, you have to call act() to run your tests correctly, but in React Testing Library you don't need to use act() most of the time since it wraps APIs with act() so you don't need to manually wrap it.

update() syncs the Enzyme component tree snapshot with the react component tree, often time you might see wrapper.update() in Enzyme tests, but React Testing Library does not need something like that, good for you since you need to handle fewer things!

Simulate user events

There are two ways to simulate user events, one is a perfect library named user-event, and the other way is to use fireEvent. user-event is actually built on top of fireEvent which simply calls dispatchEvent on the element given. However, user-event is generally recommended because it ensures that all the events are fired in the correct order for typical user interactions which helps to ensure your tests resemble the way your software is used.

To use the @testing-library/user-event module, you first need to install it:

npm install --save-dev @testing-library/user-event @testing-library/dom

Now you can import it into your test:

import userEvent from '@testing-library/user-event'

To demonstrate how to use user-event library, imagine we have a component named Checkbox, and it only shows a checkbox, and we want to simulate the user event with this component, here is the component:

// Checkbox.js
import React from 'react'
const Checkbox = () => {
return (
<div>
<label htmlFor="checkbox">Check</label>
<input id="checkbox" type="checkbox" />
</div>
)
}
export default Checkbox

And here we want to test when a user click on the checkbox, does the value change to “checked”? So, let's see how we write a test for that case:

test('handles click correctly', () => {
render(<Checkbox />)
userEvent.click(screen.getByText('Check'))
expect(screen.getByLabelText('Check')).toBeChecked()
})

Nice! With the help of other modules provided by the Testing Library, we can test our components smoothly! To learn more about the user-event library, you can have a look at its GitHub repository

Triggering class methods in tests (wrapper.instance())

As we already discussed, we are against testing implementation details and things that users are not aware of, and we aim to test and interact with the component like how our users would.

if your test uses instance() or state(), know that you're testing things that the user couldn't possibly know about or even care about, which will take your tests further from giving you confidence that things will work when your user uses them. Kent C. Dodds

If you're unsure how to test something internal within your component, then take a step back and consider: "What does the user do to trigger this code to run." Then make your test do that.

How to shallow render a component?

Generally, you should avoid mocking out components. However, if you need to, then it's pretty trivial using Jest's mocking feature. (see our FAQ)

Last updated on by Daniel Kolev