Without changing the functionality of the program, it is possible to improve the code of a program by refactoring.
Typical refactoring operations:
@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.