feat: send mailings over MailJet smtp in dedicated worker process

tests/Email/RemoveBusTransportHeaderListenerTest.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Email;
+
+use App\Email\RemoveBusTransportHeaderListener;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mailer\Envelope;
+use Symfony\Component\Mailer\Event\MessageEvent;
+use Symfony\Component\Mime\Address;
+use Symfony\Component\Mime\Email;
+
+class RemoveBusTransportHeaderListenerTest extends TestCase
+{
+    public function testTheHeaderIsGoneFromTheDeliveredMail(): void
+    {
+        $email = $this->createEmail();
+
+        (new RemoveBusTransportHeaderListener())($this->createEvent($email, queued: false));
+
+        $this->assertFalse($email->getHeaders()->has('X-Bus-Transport'));
+    }
+
+    /**
+     * Symfony reads the header off the queued message to pick the messenger transport, so
+     * removing it here would send the mailing over the shared queue after all.
+     */
+    public function testTheHeaderSurvivesQueueing(): void
+    {
+        $email = $this->createEmail();
+
+        (new RemoveBusTransportHeaderListener())($this->createEvent($email, queued: true));
+
+        $this->assertTrue($email->getHeaders()->has('X-Bus-Transport'));
+    }
+
+    private function createEmail(): Email
+    {
+        $email = (new Email())
+            ->from('[email protected]')
+            ->to('[email protected]')
+            ->subject('Betreff')
+            ->text('Nachricht')
+        ;
+
+        $email->getHeaders()->addTextHeader('X-Bus-Transport', 'mailing');
+
+        return $email;
+    }
+
+    private function createEvent(Email $email, bool $queued): MessageEvent
+    {
+        return new MessageEvent(
+            $email,
+            new Envelope(new Address('[email protected]'), [new Address('[email protected]')]),
+            'mailing',
+            $queued
+        );
+    }
+}