[TIP] how to test "impossible" events

[Tim Ottinger]

Andrew Dalke wrote:
> Perhaps I can rephrase my question.  I know how to write mock systems  
> for all of the things I've talked about.  the question I've been  
> thinking about as I write this code is the trade-off between:
>
>    - do I write code to test for cases that aren't known to occur,
>        based on experience that other similar code has done unexpected
>        things during rare circumstances?
>   
Maybe. If you think they're important cases.
>    - if so, do I test the code paths?  
If you test before coding, you can't possibly do code paths.  If you test
last, I suppose you can.  It is really like insurance; you should have all
the coverage you need: it's just hard to be sure how much you need.
> Should I
>
>        - do manual tests that the code path executed suffice?
>   
Once. To see how it works.  Then never again.
>        - or should I automate those tests?
>   
Yes.
>    - How much time should I spend setting up mock tests for
>           something that isn't known to ever occur?
>   
Insurance: as much as you honestly believe you need.  If you're short, 
you'll
*maybe* pay for more later.   If you're long, then you'll never have 
that time
back again.

I would say to keep testing and develop that sense of "enough".  But never
plan to repeat manual tests.  It's a losing game.