N°2651 rollback gitignore for lib tests dirs

Too dangerous ! We'll work properly on this but for 2.8

lib/symfony/http-kernel/Tests/Exception/NotFoundHttpExceptionTest.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Symfony\Component\HttpKernel\Tests\Exception;
+
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+class NotFoundHttpExceptionTest extends HttpExceptionTest
+{
+    protected function createException()
+    {
+        return new NotFoundHttpException();
+    }
+}