It is a method of debugging code by explaining the logic, line-by-line, out loud to an inanimate object. This often helps the programmer spot their own mistakes.

Hidden test cases usually test extreme edge cases, very large inputs (causing integer overflow), or empty inputs that your logic failed to account for.

Use a debugger to step through the code, or insert print statements to check variable values at different stages to see where the logic diverges from your expectation.