create his classes  so they can easily be re-
used. Black Box is frequently mentioned in testing. BlackBox refers
to knowing the input and output without knowing the inner workings of
the class. Another programmer can take Tim's class  and use it in
thier program  without worrying about how it works, just that it works
correctly. Of course Tim can re-use his class in other programs as
well. The class should be a free standing component. By contrast,
White Box aka "Glass Box" refers to knowing the code inside the
class.