system-tests/test/server_sent_events_spec.js

const SseStream = require('ssestream')
const systemTests = require('../lib/system-tests').default

let clients = 0

const onServer = function (app, srv) {
  app.get('/clients', (req, res) => {
    return res.json({ clients })
  })

  app.get('/foo', (req, res) => {
    return res.send('<html>foo></html>')
  })

  return app.get('/sse', (req, res) => {
    return req.socket.destroy()
  })
}

const onSSEServer = (app) => {
  return app.get('/sse', function (req, res) {
    let int

    clients += 1

    res.on('close', () => {
      clearInterval(int)
      clients -= 1
    })

    res.set({
      'Access-Control-Allow-Origin': '*',
    })

    this.sseStream = new SseStream(req)
    this.sseStream.pipe(res)

    let i = 0

    int = setInterval(() => {
      i += 1

      return this.sseStream.write({
        data: `${i}`,
      })
    }
    , 100)
  })
}

const onSSEsServer = function (app) {}

describe('e2e server sent events', () => {
  systemTests.setup({
    servers: [{
      port: 3038,
      static: true,
      onServer,
    }, {
      port: 3039,
      onServer: onSSEServer,
    }, {
      port: 3040,
      onServer: onSSEsServer,
    }],
  })

  // https://github.com/cypress-io/cypress/issues/1440
  systemTests.it('passes', {
    browser: '!webkit', // TODO(webkit): fix+unskip
    spec: 'server_sent_events.cy.js',
    snapshot: true,
  })
})