That’s a good question. I’ve taken a few tests before but just for the sake them. I’m not really sure they can properly measure your progress. I’ve met people who got 8.0 on their IELTS but still couldn’t express themselves in a natural way.
For me, it’s more about whether or not you can interact with native speakers without them getting bored just after 5 minutes of your conversation, meaning that you can understand and respond appropriately to whatever is being said.