[clug] PSIG last night

David Schoen neerolyte at gmail.com
Fri Nov 14 22:53:40 GMT 2008

I think only small (unit level) tests make sense with unit testing. Testing
that an object is still around in the DB in 6 months doesn't really help, if
the test does fail what will you do? Writing multiple tests that cover the
same thing is probably what you want.

E.g. write one test that creates a new object and test that it's immediately
accessible as suggested, but if you have atomic commits (or if testing is
done in a single user environment) you could also ensure that the number of
objects in the DB is 1 higher then what it was before you created the new
object. You could also test that when you modify something pre-existing that
the number of objects in the DB doesn't change.

This way you've already begun to isolate the problem, if either of those
tests fail there should be only a small portion of the code base responsible
for the bug, but if the object goes missing "sometime in a 6 month window"
all you know is "we have a bug somewhere in the system", a fact that can be
generally assumed for any reasonably large code base :).

I don't know anything about Django and haven't yet made it to a PSIG
meeting, this is just my opinion, take it how you will.

- Dave.

On 11/15/08, Paul Wayper <paulway at mabula.net> wrote:
> Hash: SHA1
> Alex Satrapa wrote:
> | Has anyone from the PSIG (testing in Django) last night tried writing
> | tests today?  :)
> I did :-)
> I'm still struggling with some of the philosophy behind testing, however.
>  For
> example, with Django you can have a field with a maximum length.  I'm
> assuming
> that I don't have to test that it doesn't accept strings longer than that
> (because I assume Django's testing framework already does).  Should I see
> whether it can accept unicode characters?  Should I test whether it's
> resilient to \0 characters?  Should I do this with every CharField I have
> in a
> model?  And so on with integers?  I can see that those are probably tests
> already handled in Django - but the philosophical question is whether I
> have
> to check whether Django's working or not.  Sometimes a subtle bug might
> show
> through one of those assumptions.
> OTOH the tests in the framework seem strangely simple - e.g. create a new
> object, save it in the database, and immediately retrieve it.  Surely the
> problem I'm wanting to test for is whether that record is still in the
> database six months from now, or that no-one can change the ID field of
> this
> object through the web interface?
> Don't get me wrong, I can see the value of unit tests.  I can see how
> test-driven development makes a lot of sense when you're trying to make an
> algorithm that processes data according to a variety of complex rules.  The
> testing frameworks that Paul Leopardi was talking about for testing Sage
> are
> vital so that mathematicians can know that the results are correct.  I hate
> it
> when I go and change something seemingly innocuous and find out it had deep
> consequences that a testing framework could have told me about right away.
> I'm just struggling to get exactly how it applies.
> Anyway, have fun,
> Paul
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