Add slack support to Firefly III

app/Notifications/Admin/TestNotification.php

@@ -25,6 +25,7 @@ namespace FireflyIII\Notifications\Admin;
 use FireflyIII\Mail\AdminTestMail;
 use Illuminate\Bus\Queueable;
 use Illuminate\Notifications\Messages\MailMessage;
+use Illuminate\Notifications\Messages\SlackMessage;
 use Illuminate\Notifications\Notification;
 
 /**
@@ -54,7 +55,7 @@ class TestNotification extends Notification
      */
     public function via($notifiable)
     {
-        return ['mail'];
+        return ['mail', 'slack'];
     }
 
     /**
@@ -69,6 +70,16 @@ class TestNotification extends Notification
             ->markdown('emails.admin-test', ['email' => $this->address])
             ->subject((string) trans('email.admin_test_subject'));
     }
+    /**
+     * Get the Slack representation of the notification.
+     *
+     * @param mixed $notifiable
+     * @return SlackMessage
+     */
+    public function toSlack($notifiable)
+    {
+        return (new SlackMessage)->content((string)trans('email.admin_test_subject'));
+    }
 
     /**
      * Get the array representation of the notification.