What are some common methods for simulating and testing the functionality of PHP scripts that rely on $_POST variables, especially in the context of background processes like PayPal notifications?

When testing PHP scripts that rely on $_POST variables, especially in the context of background processes like PayPal notifications, it can be challenging to simulate the exact conditions that trigger these variables. One common method is to create a separate testing script that manually sets the $_POST variables to mimic the data that would be sent by PayPal. This allows you to test the functionality of your script without relying on external sources.

// Simulating PayPal notification data for testing purposes
$_POST['payment_status'] = 'Completed';
$_POST['txn_id'] = '1234567890';
$_POST['receiver_email'] = 'paypal@example.com';

// Include your script that processes PayPal notifications
include 'paypal_notification_script.php';