[Mailer] fixed wrong behavior

src/Symfony/Component/Mailer/Tests/Transport/TransportsTest.php

@@ -0,0 +1,51 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mailer\Tests\Transport;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mailer\Transport\TransportInterface;
+use Symfony\Component\Mailer\Transport\Transports;
+use Symfony\Component\Mime\Header\Headers;
+use Symfony\Component\Mime\Message;
+use Symfony\Component\Mime\Part\TextPart;
+
+class TransportsTest extends TestCase
+{
+    public function testDefaultTransport()
+    {
+        $transport = new Transports([
+            'foo' => $foo = $this->createMock(TransportInterface::class),
+            'bar' => $bar = $this->createMock(TransportInterface::class),
+        ]);
+
+        $foo->expects($this->once())->method('send');
+        $bar->expects($this->never())->method('send');
+
+        $email = new Message(new Headers(), new TextPart('...'));
+        $transport->send($email);
+    }
+
+    public function testOverrideTransport()
+    {
+        $transport = new Transports([
+            'foo' => $foo = $this->createMock(TransportInterface::class),
+            'bar' => $bar = $this->createMock(TransportInterface::class),
+        ]);
+
+        $foo->expects($this->never())->method('send');
+        $bar->expects($this->once())->method('send');
+
+        $headers = (new Headers())->addTextHeader('X-Transport', 'bar');
+        $email = new Message($headers, new TextPart('...'));
+        $transport->send($email);
+    }
+}

src/Symfony/Component/Mailer/Transport/Transports.php

@@ -52,7 +52,7 @@ class Transports implements TransportInterface
         }
 
         $headers = $message->getHeaders();
-        $transport = $headers->get('X-Transport');
+        $transport = $headers->get('X-Transport')->getBody();
         $headers->remove('X-Transport');
 
         if (!isset($this->transports[$transport])) {