Jest not able to load underscore

Question

Getting error TypeError: Cannot read property '_' of undefined

at line import _ from 'underscore';

when running Jest-React testcase.

Answer 1

I have run into same error, hope this answer will help. To load an external modules / library into your Jest test suite. first you have to configure the test set up, see the example here.

see more under setupFiles

// jest.config.js
module.exports = {
  setupFiles : ["./setup-jest.js"]
}

---

// setup-jest.js
import lodash from 'lodash'
global._ = lodash

Instead lodash you can use underscore or any modules / library. Hope this will help.

Answer 2

The following works for me:

I do not like to have a jest.config.js file, so I use the configuration in package.json:

"jest": {
  "setupFilesAfterEnv": ["<rootDir>/setupJest.js"],
  ...
}

And in setupJest.js:

import _ from "underscore"
global._ = _

Answer 3

You can just configure the same in the jest.config.js itself, (No need of another file)

const lodash = require('lodash')

module.exports = {
    ... 
    globals: {
        '_': lodash
    }
};