Hey! I have been in my way of filling my weaknesses in German, so I started to look for diagnostic tests to see if they gave insightful feedback. What I am looking for are tests in the B1 level that tell me my weaknesses in specific topics of said level. For example, if I lack in subordinate clauses, adjective declension, connectors, Konjunktiv II, etc. I haven't tested these yet because I haven't had the time, but they seem promising.
Goethe Institut Test (I think this one gives more feedback on the level than mistakes in grammar)
I also found this page, also from Goethe, that has a very good compilation of sample tests for the official Goethe-Zertifikat B1. You can also find links to other level samples at the left of the page.
I will leave this post as a resource for anyone who wants to try them. However, if anyone has any tests that think could help me, I would be very grateful. :)