From: Mark Wilson <mwilson13@...>
Date: 2003-09-04T12:05:21+09:00
Subject: Re: [OT] Unit Tests and Encapsulation

I know nothing about bezier curves or drawing programs, so this may not 
be helpful. I'm also not an expert on unit testing, so others may have 
more useful input. Anyway...

On Wednesday, September 3, 2003, at 10:42 PM, Scott Thompson wrote:

> [snip]
> The problem is that once you have constructed the path, there is no 
> way in the public interface (at least not at the moment) for you to go 
> back and examine the points in the path.
> [snip]

I think that for unit testing purposes you don't care whether the 
interface is public or private, you test it anyway. I don't know if 
Test::Unit has a mechanism for gaining access to private methods or if 
you have to remove privacy for the duration of the tests.

> One means of making a more meaningful Unit Test would be to allow the 
> unit test to access the points of the curve (the control polygon for 
> fellow math geeks) and verify that the resulting polygon matches the 
> one that the drawing commands should produce.  Adding the routine to 
> examine the control polygon, however, would be a violation of the 
> encapsulation (or more to the point the current design of the class 
> which states that the control polygon not be available) of the 
> BezierContour class.

I don't know how your class works, but if it's monolithic (there is no 
interface to the control polygon outside of the object) I think your 
choices are (1) to temporarily add an interface for testing purposes or 
(2) decouple the elements of the class in order to expose an interface 
or (3) write the test to compare the produced object (i.e., by 
comparing a previously prepared file with the specified curve to a file 
produced by invoking the object with test input data). The last test is 
a big leap because it looks at the final product and not intermediate 
functionality.

> [snip]

> The question I have, however, is one of style.  Is this kind of class 
> extension often done in Unit Testing or is it more likely that the 
> Unit Test would only test the common public interface for the class.

I think the most usual approach is to test all interfaces (public and, 
at least initially during development, private) and to decouple 
functional elements of objects as much as possible during the 
development process. Most important though, is to write a test first 
and then implement it and then write another test and so on. If one 
writes the test first, concerns about encapsulation usually evaporate 
because the only concern in writing the test case is the interface.

> [snip]

Regards,

Mark