Stubbing the fetch API with sinon

stubbing_fetch_api.js

////Constants ////////////////////////////////////////////// 

function jsonOk (body) {
  var mockResponse = new window.Response(JSON.stringify(body), { //the fetch API returns a resolved window Response object
    status: 200,
    headers: {
      'Content-type': 'application/json'
    }
  });

  return Promise.resolve(mockResponse);
}

const MOCK_JSON = {
  'your keys' : 'your values'
  };


////Sinon //////////////////////////////////////////////////

beforeEach(() => {
  let stub = sinon.stub(window, 'fetch'); //add stub
  stub.onCall(0).returns(jsonOk(MOCK_JSON));
});

afterEach(() => {
  window.fetch.restore();  //remove stub
});

////////////////////////////////////////////////////////////

great snippet! replace window with global and works like a charm in node!

I used this to stub fetch with Qunit too, like this:

QUnit.module('fetch_modules', {
  beforeEach: function(assert) {
    let stubbedFetch = sinon.stub(window, "fetch");
    stubbedFetch.onCall(0).returns(jsonOk({}));
  },
  afterEach: function(assert) {
    window.fetch.restore();
  }
});

Hope that helps someone!