Send a test mail from the admin and log why delivery failed

Form submissions marked as not sent gave no reason: the transport
exception was swallowed. Every send now goes through MailCheck, which
logs the server's answer and a hint in German to var/log/mail.log
(server lines only, no credentials). The system screen shows the mail
route, sends a test mail to any address and lists recent attempts
(ADR 121).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/SystemScreenTest.php

@@ -47,7 +47,7 @@ final class SystemScreenTest extends WebTestCase
         $this->path = tempnam(sys_get_temp_dir(), 'kant-system-');
         $url = 'sqlite:///'.str_replace('\\', '/', $this->path);
         $this->previous = [$_SERVER, $_ENV];
-        foreach (['APP_SECRET' => 'isolated-test-secret', 'DATABASE_URL' => $url, 'SITE_ORIGIN' => 'https://cms.test', 'MEDIA_DIRECTORY' => $this->path.'-media'] as $key => $value) {
+        foreach (['APP_SECRET' => 'isolated-test-secret', 'DATABASE_URL' => $url, 'SITE_ORIGIN' => 'https://cms.test', 'MEDIA_DIRECTORY' => $this->path.'-media', 'MAIL_LOG' => $this->path.'-mail.log'] as $key => $value) {
             $_SERVER[$key] = $_ENV[$key] = $value;
         }
         $this->db = ConnectionFactory::create($url);
@@ -81,6 +81,7 @@ final class SystemScreenTest extends WebTestCase
         $this->db->close();
         gc_collect_cycles();
         @unlink($this->path);
+        @unlink($this->path.'-mail.log');
         foreach (glob($this->path.'-media/*') ?: [] as $file) {
             unlink($file);
         }
@@ -359,6 +360,41 @@ final class SystemScreenTest extends WebTestCase
         self::assertStringContainsString('Migrationen stehen aus', (string) $admin->getResponse()->getContent(), 'Und es steht immer noch aus.');
     }
 
+    public function testATestMailGoesToAnyAddressAndTheScreenSaysWhatHappened(): void
+    {
+        // Umut: „Bau mal in den Backend einen Knopf ein, Testmail an Mailadresse, wo man einträgt,
+        // und wo Logs angezeigt werden, woran es liegt“ (ADR 121).
+        $client = $this->login();
+        $client->request('GET', '/admin/system');
+        $html = (string) $client->getResponse()->getContent();
+        self::assertStringContainsString('E-Mail-Versand', $html);
+        self::assertStringContainsString('Noch nichts versendet', $html);
+        $token = (string) $client->getCrawler()->filter('form[action$="/system/testmail"] input[name=_csrf_token]')->attr('value');
+
+        $client->request('POST', '/admin/system/testmail', ['_csrf_token' => $token, 'to' => 'kein-postfach']);
+        $client->followRedirect();
+        self::assertStringContainsString('keine gültige E-Mail-Adresse', (string) $client->getResponse()->getContent());
+
+        $client->request('POST', '/admin/system/testmail', ['_csrf_token' => $token, 'to' => 'umut@cms.test', 'from' => 'formular@cms.test']);
+        self::assertStringEndsWith('/admin/system#mail', (string) $client->getResponse()->headers->get('Location'));
+        self::assertEmailCount(1);
+        $mail = self::getMailerMessage();
+        self::assertEmailAddressContains($mail, 'To', 'umut@cms.test');
+        self::assertEmailAddressContains($mail, 'From', 'formular@cms.test');
+
+        $client->request('GET', '/admin/system');
+        $html = (string) $client->getResponse()->getContent();
+        self::assertStringContainsString('Testmail an umut@cms.test vom Mailserver angenommen.', $html);
+        self::assertStringContainsString('Testmail an <code>umut@cms.test</code>', $html, 'Der Versuch steht danach in „Letzte Versuche“.');
+
+        // Nur für Administratoren, und nur mit Token.
+        $client->request('POST', '/admin/system/testmail', ['_csrf_token' => 'erfunden', 'to' => 'umut@cms.test']);
+        self::assertEmailCount(0);
+        $redaktion = $this->login('editor');
+        $redaktion->request('POST', '/admin/system/testmail', ['_csrf_token' => $token, 'to' => 'umut@cms.test']);
+        self::assertSame(403, $redaktion->getResponse()->getStatusCode());
+    }
+
     private function login(string $username = 'admin'): KernelBrowser
     {
         self::ensureKernelShutdown();