Test ajax errors

fake_ajax.js

//BASIC FUNCTION

function fetchJSON (src) {
    let promise = $.ajax({
      dataType: 'json',
      url: src,
      error: function (jqXHR, response) {
        console.log('inside')
        console.log(jqXHR)
        var msg = ''
        if (jqXHR.status === 0) {
          msg = 'Not connect.\n Verify Network.'
        } else if (jqXHR.status === 404) {
          msg = 'Requested page not found. [404]'
        } else if (jqXHR.status === 500) {
          msg = 'Internal Server Error [500].'
        } else if (response === 'parsererror') {
          msg = 'Requested JSON parse failed.'
        } else if (response === 'timeout') {
          msg = 'Time out error.'
        } else if (response === 'abort') {
          msg = 'Ajax request aborted.'
        } else {
          msg = 'Uncaught Error.\n' + jqXHR.responseText
        }
        console.log('fetchJSON failed to complete JSON fetch.', msg)
      }
    })
    return promise
}

describe('testing error functionality stubbed ajax', function () {
    before(function () {
      let stub = sinon.stub($, 'ajax')
      // set it to resolve to custom response
      let fakeJqXHR = {
        responseJSON: '',
        responseText: '',
        status: 404,
        statusText: 'Not Found'
      }
    
      stub.rejects(fakeJqXHR)
    })
    after(function () {
      $.ajax.restore()
    })
    it('test error', function () {
      //use a fake url
      let results = fetchJSON('fake.com')
      results.then(result => console.log(result))
      // want result to be ' msg = 'Requested page not found. [404]' from fetchJSON error section
    })
  })