One of the first things I learnt at University back in '85:

Axiom: "Testing never proves the absence of bugs, only their presence"

Corollary: "If you haven't found any bugs, you haven't tested everything."

Anybody that believes otherwise should have their heads examined. There's a good reason the term "Magic Numbers" was introduced in the Hacker's Jargon; the best you can hope from your software is that for everyday data input/output plus some weird instances we have foreseen, the software will behave in a polite manner.