Code Complete, 2nd Edition

Bag of Testing Tricks

Why isn't it possible to prove that a program is correct by testing it? To use testing to prove that a program works, you'd have to test every conceivable input value to the program and every conceivable combination of input values. Even for simple programs, such an undertaking would become massively prohibitive. Suppose, for example, that you have a program that takes a name, an address, and a phone number and stores them in a file. This is certainly a simple program, much simpler than any whose correctness you'd really be worried about. Suppose further that each of the possible names and addresses is 20 characters long and that there are 26 possible characters to be used in them. This would be the number of possible inputs: ...