[Python-Dev] Test cases not garbage collected after run

[Martin (gzlist)]

On 14/04/2011, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
> I'd be interested to know what is keeping the tests alive even when the
> test suite isn't. As far as I know there is nothing else in unittest
> that would do that.

The main cause is some handy code for collecting and filtering tests
by name, which unintentionally keeps alive a list outside the
TestSuite instance.

There's also the problem of reference cycles involving exc_info, bound
methods, and so on that make the lifetimes of test cases
unpredictable. That's mostly a problem for systems with a very limited
allotment of certain resources such as socket handles. However it also
makes ensuring the code doesn't regress back to leaking-the-universe
more complicated as tests may still survive past the pop.

> It's either a general problem that unittest can fix, or it is a problem
> *caused* by the bazaar test suite and should be fixed there. Bazaar does
> some funky stuff copying tests to run them with different backends, so
> it is possible that this is the cause of the problem (and it isn't a
> general problem).

The fact it's easy to accidentally keep objects alive is a general
problem. If every project that writes their own little test loader
risks reverting to immortal cases, that's not really progress. The
Bazaar example is a warning because the intention was the same as
yours, but ended up being a behaviour regression that went unnoticed
by most of the developers while crippling others. And as John
mentioned, the fix hasn't yet landed, mostly because the hack is good
enough for me and the right thing is too complicated.

Martin