Re: [Boost-users] How to isolate a class under test?

Subject: Re: [Boost-users] How to isolate a class under test?
From: Richard (legalize+jeeves_at_[hidden])
Date: 2010-06-10 12:36:20

[Please do not mail me a copy of your followup]

boost-users_at_[hidden] spake the secret code
<20100609080130.21006u389wm3wotm_at_[hidden]> thusly:

>I am testing class A.  However, class A makes some calls to class B.   
>Does Boost.Test provide any "test harness" capability so that the  
>responses from class B can be canned.  I really only want to test  
>class A, not A and B together.  I hope the question makes sense.

You need to decouple the classes somehow.  The easiest way is to use
an interface to separate them, in C++ terms a pure virtual base class
for B.  In my 5-part tutorial on using Boost.Test, you can see the use
of an interface to decouple a class from its collaborator in part 4.
<http://legalizeadulthood.wordpress.com/2009/07/05/c-unit-tests-with-boost-test-part-4/>

There are lots of ways to decouple two collaborators, but I like
"Extract Interface" the best.  If for some reason your code is too
performance sensitive for an interface sitting in the middle, you can
decouple the collaborators with templates.  I give an example of how
to decouple your code from the Win32 API using templates here:
<http://legalizeadulthood.wordpress.com/2007/12/17/faking-out-the-win32-api-with-templates/>

The book "Working Effectively With Legacy Code" provides lots of good
ideas on how to decouple your system under test from its dependencies.
I wrote a review of it here:
<http://legalizeadulthood.wordpress.com/2007/04/11/working-effectively-with-legacy-code-by-michael-c-feathers/>
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