old_contents: var assert = require('assert');
  var exec = require('../').exec;
  var spawn = require('../').spawn;
  
  exec('echo hello')
      .then(function (result) {
          var stdout = result.stdout;
          var stderr = result.stderr;
  
          assert.equal(stdout.toString(), 'hello\n');
          assert.equal(stderr.toString(), '');
      })
      .fail(function (err) {
          console.error("ERROR: ", (err.stack || err));
      })
      .progress(function (childProcess) {
          console.log('[exec] childProcess.pid: ', childProcess.pid);
      });
  
  var spawnErr = '';
  
  spawn('echo', ['hello'])
      .progress(function (childProcess) {
          console.log('[spawn] childProcess.pid: ', childProcess.pid);
          childProcess.stderr.on('data', function (data) {
              spawnErr += data;
          });
      })
      .then(function (result) {
          assert.equal(result.toString(), 'hello\n');
          assert.equal(spawnErr.toString(), '');
      })
      .fail(function (err) {
          console.error("ERROR: ", (err.stack || err));
      });
  
new_contents: var assert = require('assert');
  var cp = require('../');
  
  cp.exec('echo hello')
      .then(function (result) {
          var stdout = result.stdout;
          var stderr = result.stderr;
  
          assert.equal(stdout.toString(), 'hello\n');
          assert.equal(stderr.toString(), '');
      })
      .fail(function (err) {
          console.error("ERROR: ", (err.stack || err));
      })
      .progress(function (childProcess) {
          console.log('[exec] childProcess.pid: ', childProcess.pid);
      });
  
  cp.execFile('echo', ['hello'])
      .then(function (result) {
          var stdout = result.stdout;
          var stderr = result.stderr;
  
          assert.equal(stdout.toString(), 'hello\n');
          assert.equal(stderr.toString(), '');
      })
      .fail(function (err) {
          console.error("ERROR: ", (err.stack || err));
      })
      .progress(function (childProcess) {
          console.log('[execFile] childProcess.pid: ', childProcess.pid);
      });
  
  var spawnErr = '';
  
  cp.spawn('echo', ['hello'])
      .progress(function (childProcess) {
          console.log('[spawn] childProcess.pid: ', childProcess.pid);
          childProcess.stderr.on('data', function (data) {
              spawnErr += data;
          });
      })
      .then(function (result) {
          assert.equal(result.toString(), 'hello\n');
          assert.equal(spawnErr.toString(), '');
      })
      .fail(function (err) {
          console.error("ERROR: ", (err.stack || err));
      });
  
subject: Update test