Program testing can be used to show the presence of bugs, but never to show their absence! - Edsger W. Dijkstra

Testing can only prove the presence of bugs, not their absence. –

Testing shows the presence, not the absence of bugs

Programming is one of the most difficult branches of applied mathematics; the poorer mathematicians had better remain pure mathematicians.

When we take the position that it is not only the programmer's responsibility to produce a correct program but also to demonstrate its correctness in a convincing manner, then the above remarks have a profound influence on the programmer's activity: the object he has to produce must be usefully structured.

Several people have told me that my inability to suffer fools gladly is one of my main weaknesses.