public function testExecute()
 {
     if (!class_exists('Mongo')) {
         $this->markTestSkipped("Mongo class does not exist, test skipped");
         return;
     }
     Phalcon\DI::reset();
     $di = new Phalcon\DI();
     $di->set('mongo', function () {
         $mongo = new MongoClient();
         return $mongo->phalcon_test;
     });
     $di->set('collectionManager', function () {
         return new Phalcon\Mvc\Collection\Manager();
     });
     $ret = Songs::execute("function() { return 'Hello, world!';}");
     $this->assertEquals($ret['retval'], 'Hello, world!');
 }