This seems to be a never-ending discussion… Several posts regarding this subject were put up on discussion boards before and there were several opinions about this…
My opinion is that the test case files should remain hidden… This is because people can learn A LOT more from reading editorials and seeing other people’s code instead of staring at two different output files and to their own bugged code.
Note that you can have WA for mainly two reasons here:
b) Your logic is incorrect;
On either case having the test case files can prove useful, especially, because all main tricks and subtleties of the problem had already been discussed in detail, on the editorial… Comparing your code vs. tester/setter’s code is a much more efficient way to learn that being provided with the test case files…
Especially because problems can have sometimes 10/15 files, if you think that each file as 100.000 test cases (for example) and your program fails on the last case of the last file, then what good are the test case files to you?
Please note, that all of this as already been discussed here and you can find more opinions on this topic.