Mocking the Fetch API in a Jest/JSDOM environment

mocked-fetchapi.js

global.fetch = jest.fn().mockImplementation((url) => {
  return Promise.resolve({
    json: () => {
      if (url === 'foo/bar') {
        // json successfully parsed
        return Promise.resolve({success: true});
      }
    
      // json parse error
      return Promise.reject(new Error('JSON parse error));
    }
  });
});