[gregmac]

Debugging works extremely well during an interview because:

1. Your evaluation can be interactive: you're watching them step through, can stop and ask questions about their thought process, etc. If it's a theoretical problem (ie: not on a live computer) you can even re-calibrate on-the-fly if they're really quick (maybe a lucky guess) at narrowing down the issue, or just asking "what if this happened instead, what would you do?"

2. Grading the candidate is subjective, just like the rest of the interview process.

The OP was talking in the context of college-style evaluation. I don't think you can apply either of these things to grading someone in a course. (1) doesn't scale, and (2) isn't a fair (or unbiased) way to evaluate students.

[josephg]

Sure you can.

I’ve done “prac tests” before when I was studying CS. The test happened in a computer lab. We were given some specs and had to submit programs which implemented the specs. (The specs were written in a way that grading could happen automatically).

Just do the same thing, except the student is given some code with some failing tests. Their grade is determined by how many of the bugs they can fix within the time allotted.