Re: Unit Testing in C++

James Kanze <>
Wed, 25 Jun 2008 09:18:47 -0700 (PDT)
On Jun 25, 5:08 pm, Noah Roberts <> wrote:

Ian Collins wrote:

Noah Roberts wrote:

earthwormgaz wrote:

I'd rather not have to change the original source code
just to accommodate mocking for unit tests. Is that
actually what most people end up doing?

I try not to but sometimes it's the only way. It certainly
points to strong coupling when you have to trick your
source into allowing a mock, and maybe you want to do
something about that, but sometimes that's just the way it

It's seldom if ever the only way. It might be the easy way,
bit it is definitely a design smell.

I never said it wasn't. In legacy code issues (where complete
product lines where developed and designed without unit
testing) it can certainly be the only way to get something
under test. At times like that you absolutely have to cut
corners or you can be left refactoring HUGE chunks of code
without the support of unit tests.

That's a different issue. If you're dealing with legacy code,
or even external code (like Solaris, or Linux:-)), then you
sometimes have to resort to mock functions: you may design your
socket wrapper class to support simulating all possible errors,
but Posix didn't take that into consideration when it designed
its socket interface, and if you're going to test your socket
wrapper class, you'll need to provoke all possible error returns
from the system functions---which probably means linking in a
mock library.

The original poster spoke of a problem due to three headers
being in the same directory. IMHO, either the three headers are
so closely related that they form a single unit, or they belong
in different directories. And units should be very loosely
coupled, only depending on lower units in the hierarchy, which
they can "assume" correct and tested. (As I said, you don't
create a mock std::vector.) In an ideal world, of course.

James Kanze (GABI Software)
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