Consider this question: https://codeforces.com/problemset/problem/35/D It uses non-standard IO.

Far too many times I find myself running cf submit immediately after cf test passes. It would be useful if cf test would warn me that the problem requires non-standard IO, so that I would add the corresponding freopen statements to my C++ source code before submitting the code instead of getting a RE on test 1.