Correct code/unit testing (was Re: Efficient python programming...)

[Aahz]

In article <3D03CDD2.78C01DE1 at engcorp.com>,
Peter Hansen  <peter at engcorp.com> wrote:
>
>The nastiest bugs were found by lots and lots of work, which usually
>included repeated attempts to reproduce the problem, manual runs, 
>and sometimes using a debugger.  Staring helped little.  And then,
>having found the bug, we look at the code and say "oh yeah, we 
>should have seen that." 

Not necessarily.

>Better not to put the bugs in the code in the first place, however,
>so staring or those other things won't be necessary.  Writing the 
>tests and the code together, tests first, in small iterative steps, 
>tends not to lead to buggy code.  The payback is high compared to
>staring.

Maybe.  The most difficult bug I recall tracking down turned out to
involved a web page created by a program that put a null character at
the end of an URL, like this:

    <a href="http://www.example.com/foo/bar.html\x00">

Except, of course, that looking at the page's source in the obvious ways
didn't display the damn thing.  I finally used Python to download the
page and display chunks of the pagestring.  The problem was compounded
by a bug in MS SQL Server that considered the null-ending and
non-null-ending versions of the string to be either duplicate or unique,
depending on the precise operation.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"I had lots of reasonable theories about children myself, until I
had some."  --Michael Rios