I am currently learning German and have a friend from Morocco who understands a little. Most of the time when I have a conversation in German people seem to understand what I’m trying to say. But I can’t help but wonder what my actual level of understanding is or my progress is. What in your opinion is the best way to test your skills and maybe learn from your mistakes while doing so?
The Goethe institute offers official tests which certify you whatever level of German you test for:
They also offer a guide and an online test on how to judge which of the levels your skill corresponds to and thus which tests is the most appropriate one for you.
If you are looking for a less formal way: read books and watch TV / video. Don't start with Kant or Nietzsche, but with simpler works, maybe targetting children (what about Sendung mit der Maus? I find it interesting as adult, too).