Jest: Mock the library react-native-ultimate-config

[aymkin]

One of the files has (translation setup) imports the RNUC. And the selection of the right translations is heavily relies on .env variables. During the runtime, it resolves properly:

import config from 'react-native-ultimate-config';

console.log('--- config --- ', config);

// output
// --- config ---  {
// APP_NAME: "fooBar",
// BUNDLE_ID: "com.foo.bar
// ....
// }

But if I run the test

yarn jest app/component/Component.test.tsx

the output is

--- config ---  {}

That means I need to mock the library somehow, and I did not found the proper instructions in README

Please guide me on how to implement that.

Thank you a lot

@isilher @maxkomarychev

[isilher]

Hi @aymkin! For jest, simply treat it as a native dependency and mock it. For example:

jest.doMock('react-native-ultimate-config', () => {
  return {
    APP_NAME: "fooBar",
    BUNDLE_ID: "com.foo.bar",
  }
})

[maxkomarychev]

Hi @aymkin ,

there's nothing special about mocking this library. It can be mocked with jets's module mocks. Something as simple as:

jest.mock('react-native-ultimate-config', () => ({
    APP_NAME: "fooBar",
    BUNDLE_ID: "com.foo.bar",
}))

if you got more troubles with these - please consider sharing a reproducible example. thank you.

[aymkin]

What I actually did

• in the root directory in the folder __mocks__ (sibling to node_modules) I created a file as a library name, so I got __mocks__/react-native-ultimate-config.ts
• in that file I put the following content

  
  import { ConfigVariables } from 'react-native-ultimate-config';

const ReactNativeUltimateConfig: ConfigVariables = { APP_NAME: 'foo', APP_VERSION: 'bar', BUNDLE_ID: 'baz', };

That is it, PROFIT! 

[maxkomarychev]

To be honest I'm slightly confused with how this can work at all.

Seems like some typescript definitions are not 100% accurate.

There is no exported variable ConfigVariables - there is only one default export: https://github.com/maxkomarychev/react-native-ultimate-config/blob/51e133ee0f45f157fe82475a57c9ff0b7dd79fac/index.js#L1-L6

and the default export should be mocked, not ConfigVariables. that said I have never tried to mock it myself, I need to try it.

[aymkin]

There are ConfigVaribles in node_modules/react-native-ultimate-config/index.d.ts

[maxkomarychev]

yes, that's the problem - this not a variable that is exported. it's rather ephemeral variable which exists only in typescript but no in js

[maxkomarychev]

I added example of mock here https://github.com/maxkomarychev/react-native-ultimate-config/blob/master/packages/example/__tests__/App-test.js