"I mean a large-ish block of real code from the actual domain the candidate will be working in, which will likely offer a strong candidate many opportunities fo

"I mean a large-ish block of real code from the actual domain the candidate will be working in, which will likely offer a strong candidate many opportunities for pointing out how badly it is written" That might be a bad idea. Interviews work both ways, and you could scare away the best candidates with bad code. Maybe it would be better to show them code and say, "Here's an example of code that could be improved - how would you improve it?"