GraphQL\Type\Definition\Config::enableValidation PHP Method

    public static function enableValidation($allowCustomOptions = true)
    {
        self::$enableValidation = true;
        self::$allowCustomOptions = $allowCustomOptions;
    }

// Test this using following command
// php -S localhost:8080 ./index.php
require_once '../../vendor/autoload.php';
use GraphQL\Examples\Blog\Types;
use GraphQL\Examples\Blog\AppContext;
use GraphQL\Examples\Blog\Data\DataSource;
use GraphQL\Schema;
use GraphQL\GraphQL;
use GraphQL\Type\Definition\Config;
use GraphQL\Error\FormattedError;
// Disable default PHP error reporting - we have better one for debug mode (see bellow)
ini_set('display_errors', 0);
if (!empty($_GET['debug'])) {
    // Enable additional validation of type configs
    // (disabled by default because it is costly)
    Config::enableValidation();
    // Catch custom errors (to report them in query results if debugging is enabled)
    $phpErrors = [];
    set_error_handler(function ($severity, $message, $file, $line) use(&$phpErrors) {
        $phpErrors[] = new ErrorException($message, 0, $severity, $file, $line);
    });
}
try {
    // Initialize our fake data source
    DataSource::init();
    // Prepare context that will be available in all field resolvers (as 3rd argument):
    $appContext = new AppContext();
    $appContext->viewer = DataSource::findUser('1');
    // simulated "currently logged-in user"
    $appContext->rootUrl = 'http://localhost:8080';
    $appContext->request = $_REQUEST;