fixed test side effects

src/Symfony/Component/HttpFoundation/Request.php

@@ -382,7 +382,7 @@ class Request
      * to keep BC with an existing system. It should not be used for any
      * other purpose.
      *
-     * @param callable $callable A PHP callable
+     * @param callable|null $callable A PHP callable
      */
     public static function setFactory($callable)
     {

src/Symfony/Component/HttpFoundation/Tests/RequestTest.php

@@ -1634,6 +1634,8 @@ class RequestTest extends \PHPUnit_Framework_TestCase
         });
 
         $this->assertEquals('foo', Request::create('/')->getFoo());
+
+        Request::setFactory(null);
     }
 }