code: function createUnpackedBundle() {
    fs.mkdirp(unpackedDir, err => {
      if (err && err.code !== 'EEXIST') {
        console.log(err);
        throw err;
      }
  
      let unpackedFile = path.join(__dirname, 'unpacked.js');
      let b = browserify(unpackedFile).bundle();
      b.on('error', console.error);
      let unpackedBundleFile = path.join(unpackedDir, 'unpacked-bundle.js');
      const bundleFileStream = fs.createWriteStream(unpackedBundleFile);
      bundleFileStream.on('finish', () => {
        console.log('Wrote bundled JS into ' + unpackedBundleFile);
      });
      bundleFileStream.on('pipe', () => {
        console.log('Writing bundled JS...');
      });
      bundleFileStream.on('error', console.error);
      b.pipe(bundleFileStream);
      // bundleFileStream.end();  // do not do this prematurely!
    });
  }
docs: bundle up the test-running JS