No, they make you redo it at some other point in time and definitely don't just take 3 grades off because of it and don't tell you.
Ehh...
Depends on what the test is for.
If it's a test as I know it, like something your teacher just sets to make sure you've learnt part of the subject, then the grade either doesn't matter or they'll get you to do it later.
But if it's a proper exam, it can be worth a lot.
For example (although not truly fair since I'm not taking American exams), if I were to have missed the 1 exam in my English Language GCSE, I'd have lost 60% of the grade for not turning up.
I could not retake it, as the examboard only produces 2 exams a year, one for the spring and one for retakes.
If you miss the date of the spring one, you can't take that paper again as you could be given the answer, same for the retake.
(At GCSE (General Certificate of Secondary Education) however, they don't do retakes within the year, you have to retake the entire year/course. At A Level (Advanced Level Certificate of Secondary Education), they can depending on the course, have an exam in January then retake it in March, alongside a second-half of an exam for that course.)
So, if I were to say, have missed that one exam I'd be 60% of a grade down.
That leaves me with 40% of my grade belonging to Coursework.
If that coursework was at A* grade, then overall I'd only have 40% of the marks for an entire exam course, and the highest grade I could get would be a Grade D
