How to spy on a default exported function with Jest?

Question

Suppose I have a simple file exporting a default function:

// UniqueIdGenerator.js
const uniqueIdGenerator = () => Math.random().toString(36).substring(2,         


        

Answer 1

one could also mock the import and pass the original implementation as mock implementation, like:

import uniqueIdGenerator from './UniqueIdGenerator'; // this import is a mock already

jest.mock('./UniqueIdGenerator.js', () => {
  const original = jest. requireActual('./UniqueIdGenerator')
  return {
     __esModule: true,
     default: jest.fn(original.default)
  }
})

test(() => {
  expect(uniqueIdGenerator).toHaveBeenCalled()
})