Yes, after class

Mercedes figured the best way to test her new powers was after class some time. After all, Professor Byleth was always willing to help after class.

The class took notes. Today was a black magic day, and while Mercedes preferred white healing magic, she could see the use for black magic.

As the class was dismissed, Mercedes took her shot.

"Professor?" Mercedes asked. "Would you kindly help me with something? I didn't quite understand the lecture..."

"Of course, Mercedes," Byleth said as the last Blue Lion student left. "What did you need help with?"