a class to check classLoader configuration

autoload.php

use Symfony\Component\ClassLoader\UniversalClassLoader;

$loader = new UniversalClassLoader();
<?php

$loader->registerNamespaces(array(
    'Symfony'          => array(__DIR__.'/../a/non/existent/path/to/symfony/src', __DIR__.'/../vendor/bundles'),
    'Sensio'           => __DIR__.'/../vendor/bundles',
    'JMS'              => __DIR__.'/../vendor/bundles',
));

$loader->registerPrefixes(array(
    'Twig_Extensions_' => __DIR__.'/../vendor/twig-extensions/lib',
    'Twig_'            => __DIR__.'/../vendor/twig/lib/bad/path/too',
    'Swift_'           => __DIR__.'/../vendor/swiftmailer/lib/classes',
));

$checker = new Symfony\Component\ClassLoader\UniversalClassLoaderChecker;
var_dump($checker->check($loader));

output.php

// will output:

array(2) {
  [0]=>
  string(134) "registered namespace "Symfony" does not match with path "/var/local/webroot/helios2/app/../a/non/existent/path/to/symfony/src/Symfony""
  [1]=>
  string(121) "registered prefix "Twig_" does not match with path "/var/local/webroot/helios2/app/../vendor/twig/lib/bad/path/too/Twig/""
}

UniversalClassLoaderChecker.php

<?php

namespace Symfony\Component\ClassLoader;

class UniversalClassLoaderChecker
{
    public function check(UniversalClassLoader $classLoader)
    {
        return array_merge(
            $this->checkNamespaces($classLoader),
            $this->checkPrefixes($classLoader)
        );
    }
    
    public function checkNamespaces(UniversalClassLoader $classLoader)
    {
        $errors = array();
        foreach ($classLoader->getNamespaces() as $namespace => $paths) {
            $paths = (array)$paths;
            
            foreach($paths as $path) {
                $fullPath = sprintf('%s%s%s', $path, DIRECTORY_SEPARATOR, str_replace('\\', DIRECTORY_SEPARATOR, $namespace));
                if (false === is_dir($fullPath)) {
                    $errors[] = sprintf('registered namespace "%s" does not match with path "%s"', $namespace, $fullPath);
                }
            }
        }
        
        return $errors;
    }
    
    public function checkPrefixes(UniversalClassLoader $classLoader)
    {
        $errors = array();
        foreach ($classLoader->getPrefixes() as $prefix => $paths) {
            $paths = (array)$paths;
            
            foreach($paths as $path) {
                $fullPath = sprintf('%s%s%s', $path, DIRECTORY_SEPARATOR, str_replace('_', DIRECTORY_SEPARATOR, $prefix));
                if (false === is_dir($fullPath)) {
                    $errors[] = sprintf('registered prefix "%s" does not match with path "%s"', $prefix, $fullPath);
                }
            }
        }
        
        return $errors;
    }
}