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React Testing Library

1. Introduction​

A. What is React-Testing Library?​

React-Testing Library is a light-weight solution for testing web pages by querying and interacting with DOM nodes. It is great for Component testing.

What it gives you:

  1. a render function to render a component.
  2. many ways to query the generated DOM
  3. fire events
  4. Integration with multiple frameworks (React is one of them)

(whether simulated with JSDOM/Jest or in the browser). The main utilities it provides involve querying the DOM for nodes in a way that's similar to how the user finds elements on the page. In this way, the library helps ensure your tests give you confidence that your application will work when a real user uses it.

B. What it is not​

  1. A test runner or framework.
  2. Specific to a testing framework.
  3. Does NOT provide DOM APIs. For that you'll need either Jest (i.e. @testing-library/jest-dom), Mocha + JSDOM, or a real browser.

2. Installation​

Install these:

pnpm add -D @testing-library/dom @testing-library/jest-dom @testing-library/react jest jest-environment-jsdom ts-jest

And check out how to configure jest in your project

Then, create a setup.tsx file with the contents:

import '@testing-library/jest-dom';
import { configure } from '@testing-library/react';

configure({ testIdAttribute: 'data-test-id' });

And you're ready to write Component tests! ✅

999. Tips & Tricks​

- Tip 1: Wrapping things in act unnecessarily​

// ❌
act(() => {
	render(<Example />)
})

const input = screen.getByRole('textbox', { name: /choose a fruit/i })
act(() => {
	fireEvent.keyDown(input, { key: 'ArrowDown' })
})

// ✅
render(<Example />)
const input = screen.getByRole('textbox', { name: /choose a fruit/i })
fireEvent.keyDown(input, { key: 'ArrowDown' })

Do NOT wrap render & fireEvent in act()!!!
render and fireEvent are already wrapped in act!.

- Tip 2: Do not use cleanup​

// ❌
import { render, screen, cleanup } from '@testing-library/react'

afterEach(cleanup)

// ✅
import { render, screen } from '@testing-library/react'

For a long time now cleanup happens automatically, and you no longer need to worry about it. Learn more.

- Tip 3: Not using @testing-library/user-event​

// ❌
fireEvent.change(input, { target: { value: 'hello world' } })

// ✅
userEvent.type(input, 'hello world')

- Tip 4: Using queryByRole (and friends) NOT for non-existence​

The best thing .toBeInTheDocument can do is say: "null isn't in the document" which is not very helpful.

The only reason that queryByRole and friends exist is for you to have a function to call which does not throw an error if no element is found!. It returns null if no element is found. The only reason this is useful is to verify that an element is not rendered to the page.

- Tip 5: Using waitFor to wait for elements that can be queried with find*​

// ❌
const submitButton = await waitFor(() =>
	screen.getByRole('button', { name: /submit/i }),
)

// ✅
const submitButton = await screen.findByRole('button', { name: /submit/i })

Those two bits of code are basically equivalent (find* queries use waitFor under the hood), but the second is simpler and the error message you get will be better.
Tip: use find* anytime you want to query for something that may not be available right away.

- Tip 999: Use eslint​