On Sun, May 5, 2013 at 4:29 AM, Antoine Pitrou <report@bugs.python.org> wrote:
>
> Antoine Pitrou added the comment:
>
>> OTOH it's a useful option to have in case you're tracking down
>> something that happens (or doesn't happen) when an object is collected
>
> IMO this is a good reason to implement your specific tearDown method (or call addCleanup if you prefer), possibly in a shared base class.
>
> I don't think this is a good candidate for a command-line option, it's too specialized and it's also not something which should be enabled blindly. In other words, each test case should know whether it needs a collection or not.

This is not for tests that know or expect they need a call to
gc.collect(). This is for the case where you have 500 tests that
weren't written with gc.collect() in mind, and suddenly you have a
nondeterministic failure because something goes wrong during
collection. The cause is probably many tests earlier -- and if you
could just call gc.collect() in each tearDown() it would be a cinch to
pinpoint the test that causes this. But (unless you had all that
foresight) that's a massive undertaking. However turning on the
command line option makes it trivial.

It's rare that extra collections cause tests to fail (and if it does
that's a flakey test anyway) so just turning this on for all tests
shouldn't affect correct tests -- however it can slow down your test
suite 3x or more so you don't want this to be unittest's default
behavior. Hence the suggestion of a command line flag.