id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27124	caches_setting_for_tests passes cull related options to memcached tests	Ed Morley	Ed Morley	"The cache tests have a helper named `caches_setting_for_tests()` ([https://github.com/django/django/blob/989f6108d349e0eebdc5ad26b5cb4e882cb32e47/tests/cache/tests.py#L242-L253 source]), that generates the config that is used to override `CACHES` at various points during the test run.

However it uses `_caches_setting_base`, which contains cache `OPTIONS` such as `MAX_ENTRIES` and `CULL_FREQUENCY` that are only relevant to the locmem, filesystem and database backends ([https://docs.djangoproject.com/en/1.9/topics/cache/#cache-arguments docs]).

This is problematic, since in #20892 we're going to start passing the contents of `OPTIONS` verbatim to the memcache client constructors, which causes the tests to fail like so:
{{{
ERROR: test_memcached_uses_highest_pickle_version (cache.tests.MemcachedCacheTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/home/vagrant/src/_todo/django/tests/cache/tests.py"", line 1198, in test_memcached_uses_highest_pickle_version
    self.assertEqual(caches[cache_key]._cache.pickleProtocol,
  File ""/home/vagrant/src/_todo/django/django/core/cache/backends/memcached.py"", line 169, in _cache
    self._client = self._lib.Client(self._servers, **client_kwargs)
TypeError: __init__() got an unexpected keyword argument 'MAX_ENTRIES'
}}}

As such, the cache tests need to be adjusted to only pass those options to the backends that support them.

One way of doing this might be for `caches_setting_for_tests()` to take an additional `include_cull_settings` bool parameter, which would determine whether the problematic `cull` and `zero_cull` cache keys ([https://github.com/django/django/blob/989f6108d349e0eebdc5ad26b5cb4e882cb32e47/tests/cache/tests.py#L237-L238 source]) were included. This parameter would default to `True`, but then be set to `False` in `MemcachedCacheTests`.

Thoughts?

Many thanks :-)"	Cleanup/optimization	closed	Core (Cache system)	dev	Normal	fixed			Accepted	1	0	0	0	0	0