Quote from JomboThat doesn't seem efficient though. Don't get me wrong tests do help you improve on whatever you're testing, but they're specific. Doing a full project is more of an all-around improvement. Think of it like leveling up in a RPG game. Tests will drastically raise your level for one specific thing (for example run loops), and full projects will raise your level a small amount over a wide range of things. While you're really good at run loops, you still have little experience with everything else. You're better off being good mediocre at everything than really good at one thing and eye-shatteringly bad at others. So you should start with full projects and see what your strengths and weaknesses are, and improve on your weaknesses and do better on the next one. Otherwise you're just blindly practicing. Who knows if that blood splatter will be put into effect in a full length? It's better to learn it when you get there. It's not like there's a list of criteria you have to meet before creating a full length, you have to discover them on your own.
And besides, there's more to a full length than what can be achieved through tests.
I never said that full lengths do not help you improve because they do in my short time here I have seen quite a few animators improve by doing a full length. But what you said earlier was that doing test was a bad thing to do consitently. My opinion is that a short or test can help you improve just as much as a full length. Maybe not fully and as fast as a full length could but I think test or shorts can help you just as much.