> When I say tested properly, I mean tested completely.

I am still in the learning phase, but even I know that complete testing of any complex software is practically impossible.

So, how do you guarantee completedness in "proper" testing? I know you can't without redefining the word "completely". What's your definition?

Also see Impossibility of Complete Testing[0] by Cem Kanen, co-founder of http://www.associationforsoftwaretesting.org/

[0] http://kaner.com/pdfs/impossible.pdf