End of topic tests are a very regular feature of sixth form, at least in sciences and maths. They have a few uses IMO.
The teachers can see if the class have understood the teaching, if there are still any misconceptions they need to iron out.
They are a chance for the students to get some revision done at an early stage so the pre exam revision isn't the first time they've looked at it.
As well as to give teachers a clue to predicted grades. With some subjects they'll improve their skills throughout the 2 years, with others each topic is more stand alone, so topics don't get 'harder' as such, you just learn new material. So in those subjects the grade you get in the first year is likely to be close to what you get in the end exams. If you have adequately revised...
Always a problem for my DS it seems. I don't know anything, of course. I'm hoping he matures a lot over the next 2 years. That, at least, is something he has time to improve on.