function getPluginFolders() {
  const dir = 'plugins';
  return fs.readdirSync(dir).filter(function (file) {
    return (
      fs.statSync(path.join(dir, file)).isDirectory() &&
      fs.existsSync(path.join(dir, file, 'package.json')) &&
      // Only prepare plugins with test pages.
      fs.existsSync(path.join(dir, file, '/test/index.html'))
    );
  });
}
Find the folders that contain plugins with test pages.
@returns {Array.string} A list of directories that should be processed
  for deployment to GitHub Pages.