Re: Unit Testing in C++

James Kanze <>
Tue, 24 Jun 2008 14:26:45 -0700 (PDT)
On Jun 24, 5:38 pm, earthwormgaz <> wrote:

James Kanze wrote:

It's not too clear to me what your deliverables are, but
generally, you should organize your directory structure so
that everything in a given directory can be tested together.
If you need a mock something, then that something should
normally be from a different directory, and not part of the
code being developed in the same directory.

Hmm, I'd come to think that I wanted to mock everything around
the class under test. You seem to be saying mock around the
system that includes the class under test, unless you have to
do otherwise.

It depends on the context. It's usually acceptable to use fully
tested lower level components. (You probably wouldn't want to
mock std::vector, for example.)

This is where the unit test/integration test line blurs ...

The unit test tests "units". In some cases, one class is one
unit. In other case, not. I find that putting each "unit" in a
separate directory is a good policy, so unit tests can be
implemented at the directory level.

Say then that classes B and C interface into someLib::D, you'd
provide a mock of D, and use test hooks from that?

It depends. As I said, if someLib::D is a lower
level---something you can more or less consider "system" at the
level you're working at---then just use it. Mocking becomes
important in two cases: when the other library is also part of
the application, and can't be considered stable, and when the
other library provides an interface to some external resources,
which either aren't present, or can't be suitably controlled to
generate all of your test cases.

=46rom experience, I find that in well designed applications, the
first is rather rare (but the larger the application, the more
often it occurs).

James Kanze (GABI Software)
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