node/test/parallel/test-process-redirect-warnings.js

'use strict';

// Tests the --redirect-warnings command line flag by spawning
// a new child node process that emits a warning into a temporary
// warnings file. Once the process completes, the warning file is
// opened and the contents are validated

const common = require('../common');
const fixtures = require('../common/fixtures');
const fs = require('fs');
const fork = require('child_process').fork;
const assert = require('assert');

const tmpdir = require('../common/tmpdir');
tmpdir.refresh();

const warnmod = fixtures.path('warnings.js');
const warnpath = tmpdir.resolve('warnings.txt');

fork(warnmod, { execArgv: [`--redirect-warnings=${warnpath}`] })
  .on('exit', common.mustCall(() => {
    fs.readFile(warnpath, 'utf8', common.mustSucceed((data) => {
      assert.match(data, /\(node:\d+\) Warning: a bad practice warning/);
    }));
  }));