Jest: Cannot find module '@lingui/loader!locales/de/messages.po'

[tonytoqio]

Describe the bug
When running a test using jest it fails to import the message catalog and throws the following error

Test suite failed to run
Cannot find module '@lingui/loader!locales/de/messages.po' from 'src/components/i18n/i18nService.js'

To Reproduce

import { i18n } from "@lingui/core";
import { de as dePlurals } from 'make-plural/plurals'
import catalogDe from '@lingui/loader!locales/de/messages.po';

i18n.loadLocaleData({ de: { plurals: dePlurals } });
i18n.load({ de: catalogDe.messages });
i18n.activate(DEFAULT_LANGUAGE);

export default i18n;

Expected behavior
That the message.po catalog is imported without any error

• jsLingui version @lingui/loader@3.8.10
• Jest version jest@29.0.3
• Babel version @babel/core@7.14.3
• Your Babel config

{
  "presets": [
    "@lingui/babel-preset-react",
    [
      "@babel/preset-env"
    ],
    [
      "@babel/preset-react",
      {
        "runtime": "automatic"
      }
    ]
  ],
  "plugins": [
    "macros",
    "@babel/plugin-syntax-dynamic-import",
    "@babel/plugin-proposal-class-properties",
    "@babel/plugin-transform-async-to-generator"
  ],
  "env": {
    "test": {
      "plugins": [
        "dynamic-import-node"
      ]
    }
  }
}

[thekip]

@lingui/loader! syntax in @lingui/loader!locales/de/messages.po import is Webpack specific and would not work in Jest.

You either should compile your catalogs beforehand with lingui compile and import compiled js files or write a special module mapper for jest which will replace actual catalogs to some mocks.

Something like (I did not test that):

/** @type {import('ts-jest/dist/types').InitialOptionsTsJest} */
module.exports = {
  moduleNameMapper: {
    '^@lingui/loader!': '<rootDir>/path/to/mock',
  },
// ...
};

[thekip]

@andrii-bodnar I think some action points still needed here. Indeed if you use loader (webpack/snowpack/vite/etc) and don't have explicit compile step in your pipeline it is not that straightforward how to setup testing with jest. Compile catalogs before running tests and have separate setup for loading? Looks very complicated. I would suggest implement official transformer for jest the same way as loader works to be more aligned with the rest of tooling.

[andrii-bodnar]

@thekip thanks for the details! Reopened the issue

[gvillenave]

@thekip is addressing this still on the roadmap? Thanks!

[thekip]

Not really. I personally test only with default language, others could just mock catalogs with stubs to make tests more independent of translations and thus more reliable. So i think using a transformer to compile catalogs in Jest would bring more harm them help.