Provide a way to specify test environment setup file for Jest

My App is using localStorage but when I run tests, I get this error:

ReferenceError: localStorage is not defined

Should we provide a polyfill to be able to mock it with Jest ?

Workaround

Add a --setupTestFrameworkScriptFile ./localStoragePolyfill.js to the test command in package.json, where ./localStoragePolyfill looks like this:

const localStorageMock = (() => {
  let store = {}
  return {
    getItem(key) {
      return store[key]
    },
    setItem(key, value) {
      store[key] = value.toString()
    },
    clear() {
      store = {}
    }
  };
})()

global.localStorage = localStorageMock

I guess it should be added to config/polyfills.js.

I can PR if that’s fine. Not sure if we should use a simple inline polyfill or use something like node-localstorage though.

[gaearon]

This makes sense. I propose the following: if src/setupTests.js exists it should be used, otherwise we don’t pass it. This logic would live in createJestConfig.js. Path itself would be determined in paths.js.

@gaelduplessix Would you like to submit a PR implementing this?

[gaearon]

Thanks for fixing this!