minor #7521 Added a note about redirections to absolute URLs in tests (javiereguiluz)

This PR was squashed before being merged into the 2.7 branch (closes #7521).

Discussion
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Added a note about redirections to absolute URLs in tests

This fixes symfony/symfony#21189

Commits
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8414fb7 Added a note about redirections to absolute URLs in tests

Author: xabbuh

testing.rst

@@ -285,8 +285,9 @@ document::
 
         // Assert that the response is a redirect to /demo/contact
         $this->assertTrue(
-            $client->getResponse()->isRedirect('/demo/contact'),
-            'response is a redirect to /demo/contact'
+            $client->getResponse()->isRedirect('/demo/contact')
+            // if the redirection URL was generated as an absolute URL
+            // $client->getResponse()->isRedirect('http://localhost/demo/contact')
         );
         // ...or simply check that the response is a redirect to any URL
         $this->assertTrue($client->getResponse()->isRedirect());