Re: How did you learn your debugging skills?

From: Aggro (spammerdream_at_yahoo.com)
Date: 06/28/04 

Date: Mon, 28 Jun 2004 11:55:46 GMT

Willem wrote:

> Nonsense, not all bugs crash a program or fail a test. Lots of bugs only
> become apparent when very specific conditions arise. Very specific input,
> usually.

I got a good example of this. I had a dialog, where there were "save"
and "close" buttons. When I tested it,
1. I made changes,
2. pressed save
3. and then close
4. and then opened dialog again
5. And checked that things were saved and loaded properly.

Now, when customer tried it, she did:

1. Made changes.
2. Pressed save
3. Made changes
4. Pressed save
5. Made changes
(You see the pattern here, don't you?)

And it turned out, that the the program didn't work correctly when save
was pressed multiple times before closing. Program had something like a
container, where all data was saved when save was pressed, and then
content of the container was saved to database. Container was never
cleared after the saving, so every time save was pressed, amount of data
in container increased.

So no crashing, and all tests passed, and still there was a bug. (Very
easy to debug and fix after it was found.)

Much harder things to debug have been bugs in Microsoft API libraries,
that have appeared only on certain conditions and usually only after
several hours of use. It is _a lot_ easier to find bugs in your own
code, that finding it on someone elses code, especially if you can't see
the code. These things I have debugged by creating small test
applications that use those API functions to see what happens.