Free Rice is a great site where you can take endless vocabulary tests!
If you don't like vocabulary, you can take everlasting multiple choice tests on Art, Chemistry, Geography, Language Learning, and Math. Every time you get an answer right, the site donates 10 grains of rice to the World Food Programme. It is so good.
The other day, a certain person I was speaking with asked me what my highest level was, and I said 48 out of 60, which I was not sure was true. It lead to terrible confessions about me being a liar all the time, which is a fact. So I played on Free Rice this evening until it was true. This is my screenshoot proof.