Re: C++ fluency

James Kanze <>
Fri, 8 May 2009 02:47:31 -0700 (PDT)
On May 7, 9:56 pm, Ian Collins <> wrote:

Phlip wrote:

James Kanze wrote:

That would be impressive. In the well run companies I've
worked in, the bug rate was generally less than 1 per 100
KLOC of code going into integration. You're saying that
TDD will give bug rates of less than one error per million
lines of code?

No - the 10% metric goes from Waterfall or Code-n-Fix to
TDD. Not from excessive unit testing to TDD.

I think these "well run companies" (ie companies that people
like Ian, Noah, or me are not smart enough to run) would
still achieve a much higher velocity. And I also question
the definition of "bug". If it's "divergence from the
specification", then you might be underrepresenting the
other definition - "features the users don't like". That
rate will go down as your velocity goes up and you deploy
more often, in smaller feature increments.

I think that's the key - teams using TDD and the other XP
practices can achieve impressive error rates in a shorter time
than teams employing after the fact unit tests and extensive
code review.

Then why aren't they doing it? Why aren't the companies
actually producing high quality code efficiently using TDD?

It may be possible with sufficient vigour to get the same test
coverage with after the fact tests, but they will take a lot
longer to write and may require code coverage tools for
verification. One of the big benefits if TDD is it makes
testing an enjoyable part of the process rather than a chore.

I won't deny that there may be psychological benefits in some
cases. Although I find a lot of satisfaction in participating
in teams where we get zero errors from the field, having
delivered on time and in budget.

James Kanze (GABI Software)
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