node/test/parallel/test-net-listen-exclusive-random-ports.js

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

function noop() {}

if (cluster.isMaster) {
  const worker1 = cluster.fork();

  worker1.on('message', function(port1) {
    assert.strictEqual(port1, port1 | 0, 'first worker could not listen');
    const worker2 = cluster.fork();

    worker2.on('message', function(port2) {
      assert.strictEqual(port2, port2 | 0, 'second worker could not listen');
      assert.notStrictEqual(port1, port2, 'ports should not be equal');
      worker1.kill();
      worker2.kill();
    });
  });
} else {
  const server = net.createServer(noop);

  server.on('error', function(err) {
    process.send(err.code);
  });

  server.listen({
    port: 0,
    exclusive: true
  }, function() {
    process.send(server.address().port);
  });
}