simulate-500-error.php

<?php
/**
 * Plugin Name: Simulate 500 Internal Server Error
 * Description: Prints out a typically-looking PHP error when display_errors is enabled. To use, simply add <code>?internal_server_error</code> to any URL.
 * Author: Weston Ruter
 * Plugin URI: https://gist.github.com/westonruter/9b7330fffd24dd61aa1519004a2608b1
 * Version: 1.0
 * License: GPLv2 or later
 *
 * @package Simulate500Error
 */

add_action( 'init', function() {
	if ( ! isset( $_GET['internal_server_error'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.NoNonceVerification
		return;
	}
	header( 'X-Robots-Tag: noindex' );
	status_header( 500 );

	printf( "<br />\n<b>Example error</b>: nothing bad happened, but this prints an error for testing purposes in <b>%s</b> on line <b>%d</b><br />\n", __FILE__, __LINE__ );
	exit;
} );