node/test/parallel/test-debug-port-from-cmdline.js

'use strict';
var common = require('../common');
var assert = require('assert');
var spawn = require('child_process').spawn;

var debugPort = common.PORT;
var args = ['--interactive', '--debug-port=' + debugPort];
var childOptions = { stdio: ['pipe', 'pipe', 'pipe', 'ipc'] };
var child = spawn(process.execPath, args, childOptions);

child.stdin.write("process.send({ msg: 'childready' });\n");

child.stderr.on('data', function(data) {
  var lines = data.toString().replace(/\r/g, '').trim().split('\n');
  lines.forEach(processStderrLine);
});

child.on('message', function onChildMsg(message) {
  if (message.msg === 'childready') {
    process._debugProcess(child.pid);
  }
});

process.on('exit', function() {
  child.kill();
  assertOutputLines();
});

var outputLines = [];
function processStderrLine(line) {
  console.log('> ' + line);
  outputLines.push(line);

  if (/Debugger listening/.test(line)) {
    process.exit();
  }
}

function assertOutputLines() {
  var expectedLines = [
    'Starting debugger agent.',
    'Debugger listening on 127.0.0.1:' + debugPort,
  ];

  assert.strictEqual(outputLines.length, expectedLines.length);
  for (var i = 0; i < expectedLines.length; i++)
    assert(expectedLines[i].includes(outputLines[i]));
}