Make tests support phpunit 8

Author: nicolas-grekas

Tests/OptionsResolverTest.php

@@ -13,18 +13,21 @@
 
 use PHPUnit\Framework\Assert;
 use PHPUnit\Framework\TestCase;
+use Symfony\Bridge\PhpUnit\ForwardCompatTestTrait;
 use Symfony\Component\OptionsResolver\Exception\InvalidOptionsException;
 use Symfony\Component\OptionsResolver\Options;
 use Symfony\Component\OptionsResolver\OptionsResolver;
 
 class OptionsResolverTest extends TestCase
 {
+    use ForwardCompatTestTrait;
+
     /**
      * @var OptionsResolver
      */
     private $resolver;
 
-    protected function setUp()
+    private function doSetUp()
     {
         $this->resolver = new OptionsResolver();
     }