Jest: test Intl.DateTimeFormat

Question

I would like to test a filter function I wrote which return a date formatted using Intl.DateTimeFormat(\'en-GB\', options):

// module \"date.js\"
export default          


        

Answer 1

The only solution that I managed to find to this problem was to install full-icu which seemed to provide the right locales to node during the testing process.

That package is needed because node by default only ships with a limited set of locales, explained here: https://nodejs.org/docs/latest-v9.x/api/intl.html

With that package installed, the additional step that I had to take was to change my test command to use:

"test": "NODE_ICU_DATA=node_modules/full-icu jest --config jest.config.js"

I ran into this problem in a couple of different environments. When running the tests locally on Mac OS and also when running the tests inside a Docker container during CI.

Interestingly, I don't need to use the export when running the tests via WebStorm's Jest integration. It definitely seems like the behaviour of the Intl library is far from stable in node.

Answer 2

In package.json add the intl package

 "intl": "*",

In the jest.config.js

module.exports = {
    moduleNameMapper: {
        Intl: '<rootDir>/node_modules/intl/'
    }
};

Then in Date.spec.js

 describe(`Date by locale`, () => {
     beforeAll(() => {  global.Intl = require('intl'); });
    // Add your tests here. 
    // Add a temporary console.log to verify the correct output
 }

Answer 3

You can use polyfill, as described here

import IntlPolyfill from 'intl';
import 'intl/locale-data/jsonp/ru';

if (global.Intl) {
    Intl.NumberFormat = IntlPolyfill.NumberFormat;
    Intl.DateTimeFormat = IntlPolyfill.DateTimeFormat;
} else {
    global.Intl = IntlPolyfill;
}