through

What does 'have ben through this before' mean?

“Well, it wasn’t too bad, was it?” asked Hermione anxiously in the entrance
hall two hours later, still clutching the exam paper. “I’m not
sure I did myself justice on Cheering Charms, I just ran out of
time — did you put in the countercharm for hiccups? I wasn’t sure
whether I ought to, it felt like too much — and on question twenty three —”
“Hermione,” said Ron sternly, “we’ve been through this before. . . .
We’re not going through every exam afterward, it’s bad enough doing
them once.”