code: function getSourceDirectories() {
  	var dirs = [ 'lib', 'src', 'app' ],
  		result = [];
  
  	dirs.forEach(function(dir) {
  		if (test('-d', dir)) {
  			result.push(dir);
  		}
  	});
  
  	return result;
  }
docs: Determines which directories are present that might have JavaScript files.
  @returns {string[]} An array of directories that exist.
  @private