React Intl

Note

If you want to combine setupTests with another setup you should check setup

Configuring React-Intl Polyfills / Locales

If you're using React-Intl in your project, and you need to load a locale, You have two options:

1. When using Node 13 and higher, Intl support is now out of the box. The default ICU (International Components for Unicode) option for Node is full-icu meaning all ICU's.
   All you need to do is embed the set of ICU data you need:

   // test-utils.js
   
   const hasFullICU = () => {
     // That's the recommended way to test for ICU support according to Node.js docs
     try {
       const january = new Date(9e8)
       const pt = new Intl.DateTimeFormat('pt', {month: 'long'})
       return pt.format(january) === 'janeiro'
     } catch (err) {
       return false
     }
   }
   
   export const setupTests = () => {
     if (hasFullICU()) {
       Intl.NumberFormat.format = new Intl.NumberFormat('pt').format
       Intl.DateTimeFormat.format = new Intl.DateTimeFormat('pt').format
     } else {
       global.Intl = IntlPolyfill
     }
   }

2. When using Node with prior versions, the ICU default option is small-icu meaning it includes a subset of ICU data (typically only the English locale).
   If you do need to load a locale you have two options:

   1. Load the Polyfills according to that language:

      // test-utils.js
      import IntlPolyfill from 'intl'
      import 'intl/locale-data/jsonp/pt'
      
      export const setupTests = () => {
        // https://formatjs.io/docs/guides/runtime-requirements/#nodejs
        if (global.Intl) {
          Intl.NumberFormat = IntlPolyfill.NumberFormat
          Intl.DateTimeFormat = IntlPolyfill.DateTimeFormat
        } else {
          global.Intl = IntlPolyfill
        }
      }

   2. Load the ICU's at runtime:
      Install the package full-icu and inject it to your test environment, you can do that by setting NODE_ICU_DATA before calling jest: NODE_ICU_DATA=node_modules/full-icu jest. Doing that you will give you full-icu support as shown in option 1.

Creating a custom render function

To test our translated component we can create a custom render function using the wrapper option as explained in the setup page.
Our custom render function can look like this:

// test-utils.js
import React from 'react'
import {render as rtlRender} from '@testing-library/react'
import {IntlProvider} from 'react-intl'

function render(ui, {locale = 'pt', ...renderOptions} = {}) {
  function Wrapper({children}) {
    return <IntlProvider locale={locale}>{children}</IntlProvider>
  }
  return rtlRender(ui, {wrapper: Wrapper, ...renderOptions})
}

// re-export everything
export * from '@testing-library/react'

// override render method
export {render}

A complete example

import React from 'react'
import '@testing-library/jest-dom'
// We're importing from our own created test-utils and not RTL's
import {render, screen, setupTests} from '../test-utils.js'
import {FormattedDate} from 'react-intl'

const FormatDateView = () => {
  return (
    <div data-testid="date-display">
      <FormattedDate
        value="2019-03-11"
        timeZone="utc"
        day="2-digit"
        month="2-digit"
        year="numeric"
      />
    </div>
  )
}

setupTests()

test('it should render FormattedDate and have a formatted pt date', () => {
  render(<FormatDateView />)
  expect(screen.getByTestId('date-display')).toHaveTextContent('11/03/2019')
})

Translated components testing stategy

When testing a translated component there can be different approaches for achieving the wanted coverage, where the aimed goal should be to allow testing the component in a way that will simulate the user behavior as much as posible.

Approach	Pros	Cons
Use strings from the default language	Test is easy to read, and asserts expected default output. If you have variables in your strings, you can test that they work properly with correct output.	1. Strings hardcoded into tests mean you have to update both tests and code for any copy changes. 2. If multiple elements have the same string/substring text, find-and-replace may be hard to use reliably.
Mock the translation library	If your library is difficult to use in the test environment, you can mock it so it is easier. For example, you can add the message ID as a data-attribute to the text so you can query by that.	Test code deviates from what runs in production. Tests may assert about message IDs but not enough about content, so errors are possible.
Use translation library in tests	Decouples strings from tests, so you can update the message files in one place without worrying about breaking tests. Can run tests in another language or multiple languages. const buttonText = getNodeText(<FormattedMessage id="buttonText" defaultMessage="Hello Button" />);	Overhead - it takes more lines of code to write the test, and you need to know the variables and message IDs to create the right strings. It's not obvious what the text actually is when you read the test code, making maintaining it harder.
Use translation library + inline snapshots	Same as above, but by adding an inline snapshot of the string, you can read the test code and see what strings are in use, but easily update them with jest --updateSnapshot if the messages change. expect(buttonText).toMatchInlineSnapshot("'My button text'")	Tests are longer because of the extra lines. You can wrap up some of the translation-related code into a helper function to make it a little more inline-able and avoid repeating yourself, but you still need to know the message IDs and variables inside the test.