node/test/parallel/test-child-process-stdout-flush.js

'use strict';
const common = require('../common');
const assert = require('assert');
const path = require('path');
const spawn = require('child_process').spawn;
const sub = path.join(common.fixturesDir, 'print-chars.js');

const n = 500000;

const child = spawn(process.argv[0], [sub, n]);

let count = 0;

child.stderr.setEncoding('utf8');
child.stderr.on('data', common.fail);

child.stdout.setEncoding('utf8');
child.stdout.on('data', (data) => {
  count += data.length;
});

child.on('close', common.mustCall((code, signal) => {
  assert.strictEqual(code, 0);
  assert.strictEqual(signal, null);
  assert.strictEqual(n, count);
}));