Re: C++ fluency

James Kanze <>
Fri, 8 May 2009 02:26:01 -0700 (PDT)
On May 7, 5:15 pm, Noah Roberts <> wrote:

James Kanze wrote:

The second reason is on principle. In TDD you're not
supposed to write ANY code that isn't guided by a test

So what do you do about things which can't be thoroughly
tested? Like thread safety, or most floating point.

Any theory that answers everything, answers nothing.


I don't know. I don't know of anyone who's come up with an
answer either.

And yet, there are multithreaded programs which work correctly.
(Admittedly, not very many.) And programs using floating point
which work correctly.

In the case of floating point, there is a large body of theory
and knowledge, which permits formal proofs in some cases (but
the validity of the proofs still has to be verified). In both
cases (and in every other case I know, for that matter), if you
want quality software, you use a combination of methods:
testing, code review, etc., etc. No one tool is perfect, and
each more or less verifies the others.

Another aspect of TDD though is that it isn't just a
development guiding process but also a design guiding

And how do you design the tests? Or rather, how do you
define what the tests should test? At some point, your
client or user specifies a problem, not a series of tests,
and you have to "design" something (not necessarily even a
program) which solves that problem.

Not sure what your question is. You seem to have answered it
yourself: user requirements.

But my user requirements are in terms of e.g. Implement the
protocol defined in RFC xxx. The resulting program must be able
to handle n requests per minute on machine x. The following
logging will be supported... From that, I need to design, to
determine what classes are needed, etc. It's not until I've
specified the requirements for each class in detail that I can
start thinking about unit tests.

James Kanze (GABI Software)
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