Illustrating how one can orchestrate mocks using dependency injection

DependencyInjection.js

function work_ (url, {UrlFetchApp_=UrlFetchApp}={}) {
  Logger.log(url);
  return UrlFetchApp_.fetch(url).getContentText();
}

function testWork() {
  const url = 'https://example.com';
  const response1 = work_(url);
  Logger.log(response1); 
  class Mocked {
    static fetch() {
      return {
        getContentText: () => 'ha'
      };
    }
  }
  const response2 = work_(url, {UrlFetchApp_: Mocked});
  Logger.log(response2);
}