Without changing the funtionality of the program, it is possible to change code of the programe by refactoring.
@tunixman: if there is no unit test, why should we use refactorings?
@bigballofmud BrianFoote: Technically yes, but so is blindfolded brain surgery.
You unit test guys crack me up. You're like heroin junkies, but funnier.
See WhatIsRefactoring for a more complete description and explanation.