json中如何将key中的引号去掉

function my_json_decode($str) {        //
$str = preg_replace('/"(\w+)"(\s*:\s*)/is', '$1$2', $str);   //去掉key的双引号
return $str;
}
$str = '{"test":[{"testName":"哈哈","Url":"http://www.test.com"}]}';
$str = my_json_decode($str);
echo $str;