jest mock node-fetch

getUsers.js

const fetch = require('node-fetch')

const getUsers = () => fetch('https://reqres.in/api/users')
    .then(res => res.json())

module.exports = getUsers

getUsers.test.js

const getUsers = require('./getUsers')
const fetch = require('node-fetch')

it('fetches users', async () => {

  const mockResponse = [
    { id: 1, name: 'Simo' },
    { id: 2, name: 'Massimo' },
  ]

  fetch.mockResponse(JSON.stringify(mockResponse))

  expect(await getUsers()).toEqual(mockResponse)

})

package.json

{
  "dependencies": {
    "jest": "^22.2.1",
    "jest-fetch-mock": "^1.4.1",
    "node-fetch": "^2.0.0"
  },
  "scripts": {
    "test": "jest"
  },
  "jest": {
    "setupFiles": [
      "./setupJest.js"
    ]
  }
}

setupJest.js

const fetch = require('jest-fetch-mock')
jest.setMock('node-fetch', fetch)

JestObject - here it's say it ok