I have always been a fan of integrated debuggers. They really help me think about tricky bits of code and verify that my solution is correct. While testing my code I like to use a debugger to watch all my variables and boolean conditions. Sometimes during a walk through like this I will see some problem with a variable value that isn't manifesting to the user with any of my chosen test cases but could occur in the real world.
Here is what it looks like when I run it against the front page of NITRC: