Mocking Fetch API by using Jest

mockFetch.js

/**
 * Minimal mocking
 */
 
// `global` is available in both node and browser environment

/*
global.fetch = () => 
  Promise.resolve({
    json: () => Promise.resolve({
      foo: 'bar',
    })
  })
*/

/**
 * Jest mocking
 */

describe('Testing', () => {
  beforeAll(() => {
    jest.spyOn(global, 'fetch')
  })
  
  beforeEach(() => {
    /*
    global.fetch.mockImplementation(() =>
      Promise.resolve({
        json: () => Promise.resolve({
          foo: 'bar'
        })
      })
    )
    */
    
    global.fetch.mockResolvedValueOnce({
      json: () => {
        foo: 'bar'
      }
    })
  }
})
 
// expect(global.fetch).toHaveBeenCalledTimes(1)
// expect(global.fetch).toHaveBeenCalledWith('url://')