e2e-test.js

import Server from 'server';
import Logger from 'logger';
import Slack from 'slackNotifier';
import sinon from 'sinon';

it('should log startup errors and send them to slack', () => {
  sinon.spy(Logger, 'logException');
  Slack.notify = sinon.spy(() => {});
  
  Server.create({ port: 5000 });
  Server.create({ port: 5000 }); // port already taken
  
  expect(Slack.notify).to.be.called();
  expect(Logger.logException).to.be.called();
});