"Program testing can be used to show the presence of bugs, but never to show their absence!"

This quote by Edsger Dijkstra is a reminder that program screening is a helpful tool, however it has its restrictions. Program screening can be used to identify bugs in a program, however it can not ensure that there are no bugs present. This is due to the fact that it is impossible to test every possible combination of inputs and outputs, and it is likewise hard to anticipate how a program will behave in specific circumstances. For that reason, program screening can only show the presence of bugs, not their absence. This suggests that even after comprehensive screening, there might still be bugs present in the program that have actually not been determined. This highlights the value of thorough screening and the need for designers to be aware of the limitations of program screening.