Re: class design: where to put debug purpose utility class?

James Kanze <>
Fri, 27 Jun 2008 11:50:06 -0700 (PDT)
On Jun 27, 4:15 pm, Joe Greer <> wrote:

SeanW <> wrote

On Jun 27, 8:56 am, Joe Greer <> wrote:

Greg Herlihy <> wrote in

There should not be any code added to foo's public API
for unit testing purposes.

2. I want the function class to be independent from test class

Yes, the unit test should be completely independent from the
interface being tested (in other words, the unit test should just
be another client of foo - and nothing more).

I wouldn't necessarily disagree with this, but I seem to have a lot
of classes whose primary goal is a side effect. For example a writer
to a file. By design, there really isn't any feedback to the client
of the class, it just works or throws. If I just treat things as a
normal user, I have no way of knowing directly if the data made it to
the file or if there was a error that wasn't reported properly. How
do you usually test such cases or is that another class of test that
isn't called a 'unit test'?

I would just reach around in that case:

  test_object.append("some.file", "SOME-STRING");
  assert(system("tail -n 1 some.file | grep -q '^SOME-STRING$'") ==

Or something along those lines.

Yes. but that wouldn't be using my class' public interface. I
can see a lot of different ways to check it outside the class,
but is that still within Greg's definition of a unit test?

I don't see why not. The "public" interface of the class is
what is visible from outside the class. Data written a file is
(hopefully) visible, and thus part of the public
interface---part of the post-condition. (I have some cases
where the "post-condition" is a core dump; I also have unit
tests which verify this.)

James Kanze (GABI Software)
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