Jest: TypeError: Cannot read property 'registerLocale' of undefined

[asode]

Hi, I was wondering what am I doing wrong here as I'm trying to test my component with jest. In browser it works fine. Should I somehow exclude the language imports from jest run as it doesn't run in a browser (just speculating)?

node 14.17.3
npm 8.5.0

i18n-iso-countries@7.3.0
jest@27.5.1
@testing-library/dom@8.11.3
@testing-library/jest-dom@5.16.2
@testing-library/svelte@3.0.3
@testing-library/user-event@13.5.0

import countries from "i18n-iso-countries"

  // Register.svelte
  import countries from "i18n-iso-countries";
  import countriesEnglish from "i18n-iso-countries/langs/en.json";
  countries.registerLocale(countriesEnglish);

Jest outputs the following error:

TypeError: Cannot read property 'registerLocale' of undefined

      13 |   import countriesEnglish from "i18n-iso-countries/langs/en.json";
    > 14 |   countries.registerLocale(countriesEnglish);
         |             ^

      at instance (src/components/register/Register.svelte:14:13)
      at init (node_modules/svelte/internal/index.js:1865:11)
      at new Register (src/components/register/Register.svelte:604:3)
      at render (node_modules/@testing-library/svelte/dist/pure.js:81:21)
      at Object.<anonymous> (src/components/register/Register.test.ts:145:11)

---

Also tried import * (inspired by #125), but it only caused a different error:

import * as countries from "i18n-iso-countries"

  // Register.svelte
  import * as countries from "i18n-iso-countries";
  import countriesEnglish from "i18n-iso-countries/langs/en.json";
  countries.registerLocale(countriesEnglish);

Jest outputs the following error:

TypeError: Cannot read property 'locale' of undefined

      13 |   import countriesEnglish from "i18n-iso-countries/langs/en.json";
    > 14 |   countries.registerLocale(countriesEnglish);
         |             ^

      at Object.<anonymous>.exports.registerLocale (node_modules/i18n-iso-countries/index.js:99:19)
      at instance (src/components/register/Register.svelte:14:13)
      at init (node_modules/svelte/internal/index.js:1865:11)
      at new Register (src/components/register/Register.svelte:607:3)
      at render (node_modules/@testing-library/svelte/dist/pure.js:81:21)
      at Object.<anonymous> (src/components/register/Register.test.ts:145:11)

[asode]

Got around the issue by mocking the functions:

jest.mock("i18n-iso-countries", () => ({
  default: jest.fn(),
  registerLocale: jest.fn(),
  getNames: jest.fn().mockResolvedValue({ EN: "English" }),
}));

But is this really required? Shouldn't the library work with jest even without mocking?

[Gurochka]

It seems that jest can't find localization files to insert them to registerLocale. Another solution is to add a root path to the jest.config.js file:
roots: ["<rootDir>/src", "<rootDir>/node_modules/i18n-iso-countries"].
That worked for me.