From: Hugh Sasse Staff Elec Eng <hgs@...>
Date: 2000-08-18T17:51:55+01:00
Subject: [ruby-talk:04503] RubyUnit and encapsulation.

My_class's instance variables are not all "attr :<name>" type variables,
so some can only be accessed from inside the class.  That is fine, it is
what OO is all about.

I design some RubyUnit tests for My_class, with a Testing_class to do
them.

I have 3 ways I could do this:

1 Test the external interface to My_class only.  

My tests will outlive any implementation details of My_class, but they
won't tell me too much about why they have failed, if they do.

2 Test the internals of the class.

I cannot get at these from Testing_class, but if I could I could guarantee
that each method of My_class was doing what I intended, even private
methods, so I could simplify the testing structure, and localise bugs more
easily.

3 Make more of the internals of My_class visible to the outside world

This would make 2 easier, but if I change the internals later, then my
interface changes.


It seems like 1 is the only sensible way to do this, and "If the errors
don't localise the bugs, then Tough!".  The implication seems to be that I
should redesign my class, but in what way(s)?  My class currently holds
arrays, hashes, and booleans in a unified whole. Most of the methos setup
the correct values in these as files are processed. Is such a question too
case-specific to have any useful general answer(s)?

	Hugh
	hgs@dmu.ac.uk