Blockchain API support - receive payment IPN
It is possible to test it offline. Check your phpinfo() to confirm, but I perform operations with the blockchain API from my XAMPP server all the time, as I am currently working on a site that uses the API. All you're doing is sending a request to a URL (like when you loaded this page) and getting the contents of that file. If you're interested, check out this class I wrote for using the blockchain API with PHP: https://github.com/lukesims/Blockchain-API-PHP-Class

With that, you could ad more functions or modify it to interact with your database simultaneously.