To be honest, i think when you are learning a language the most important are grammar and pronunciation, for me when you have grammar you can speak and write in a good way and pronunciation is important too because if you pronunciate something wrong (in Spanish for example) the meaning of the word changes. If you want to know how you can assess your progress I consider that you have doing a conversation club or you can practice with a native of the language that you are learning.

Success!

For me there are two ways without books or tests. I generally don't like to have a score on my progress. I'd rather have goals. Let's say my goal for the week or month would be to finally understand more than a half of a children's movie in the language I'm learning without subtitles. Or be able to read a text and memorize all its vocabulary. Being able to understand all the words or most of them will be my goal. 

With partners, they are very helpful for conversation, pronunciation, and slang. I usually read something for them and if they can understand me correctly without knowing the text, it's a new goal accomplished. I also ask them how to pronounce words. (I always assume all native speakers know how to pronounce words correctly, hence they are great pronunciation teachers).