Re: how many bugs do you find and correct during TDD?

From: Andrew McDonagh (news_at_andrewcdonagh.f2s.com)
Date: 12/31/04 

Date: Thu, 30 Dec 2004 23:21:55 +0000

Tammy wrote:
>
> H. S. Lahman wrote:
>
>> Mechanical bugs (e.g., from typos, sloppy coding practices, etc.) are
>> going to be the same regardless of how one designs the software or the
>> tests. Their incidence is directly proportional to the LOC written.
>
>
> How do you know? So TDD doesn't actually find any "real" bugs,
> it just prevents them from happening?

TDD is a design methodology whereby the systems design evolves from
tests, not from UML diagrams/meetings/Functional Specs etc. These things
do happen, but usual within the 10 min time frame rather than the usual
1 or 2 months time frame.

TDD is not used to find bugs, its used to design and implement the
application starting with a test.

It certainly prevents MOST bugs from happening - as the test code (which
is written first) must have a bug* which allows the application codes
bug to be undetected (i.e. not executed during a test run).

However, nothing can stop bugs from happening - it just helps to reduced
them, using preventative means.

The only time when TDD could be described as 'finding a bug'. Is
actually when you as a developer have found the bug manually, then
written a unittest to execute the same scenario. This test at first
fails because of the bug, then you fix the bug and the test passes.
Then because you have a test for this explicit bug, it should never
reappear.

*By bug, I mean it could be:-

eg1) A missing test scenario, and therefore the particular logic path
through the application code is not executed at test time.

eg2) The test doesn't assert anything and so finished with a success
state regardless of whether the thing under test should have failed.

eg3) ...

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