A neophyte in the software world might ask a seemingly legitimate question once all modules have been unit tested: “if they all work individually,why do you doubt that they’ll work when we put them together?”The problem,of course,is”putting them together”—interfacing.Data can be lost across an interface;one component can have an inadvertent, adverse effect on another ; subfunctions ,when combined may not produce the desired major function;individually acceptable imprecision may be magnified to unacceptable levels; global data structures can present problems.Sadly,the list goes on and on.