node/test/parallel/test-cluster-net-listen.js

'use strict';
const common = require('../common');
const assert = require('assert');
const cluster = require('cluster');
const net = require('net');

if (cluster.isMaster) {
  // ensure that the worker exits peacefully
  var worker = cluster.fork();
  worker.on('exit', function(statusCode) {
    assert.equal(statusCode, 0);
    worker = null;
  });
  process.on('exit', function() {
    assert.equal(worker, null);
  });
} else {
  // listen() without port should not trigger a libuv assert
  net.createServer(common.fail).listen(process.exit);
}