N°2651 rollback gitignore for lib tests dirs

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

lib/symfony/debug/Tests/Fixtures/LoggerThatSetAnErrorHandler.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+use Symfony\Component\Debug\BufferingLogger;
+
+class LoggerThatSetAnErrorHandler extends BufferingLogger
+{
+    public function log($level, $message, array $context = [])
+    {
+        set_error_handler('is_string');
+        parent::log($level, $message, $context);
+        restore_error_handler();
+    }
+}