>
> Are these the kind of objects you assign during setUpTestData though?
>

They're not the kind of things *I* assign but I bet somewhere out there,
some project does extensively :)

What about going through a deprecation period where non-picklable
> assignment during setUpTestData raises a deprecation warning suggesting
> using setUpClass or direct class attributes assignment?
>

I like this idea, it's actually likely to be easy to implement too (on top
of the descriptor).

On Tue, 27 Nov 2018 at 08:59, charettes <charett...@gmail.com> wrote:

> Thanks for chiming in Adam.
>
> I think this is too much of an ask for backwards compatibility. Lots of
>> things aren't deepcopy-able, as per its docs:
>>
>
> Right. Are these the kind of objects you assign during setUpTestData
> though? They could be easily moved to setUpTestCase for example.
>
> How about adding a container object to TestCase, which deepcopy()'s its
>> attributes on setUp. It could be called something short like "data', which
>> would make your example:
>>
>
> That seems like a viable alternative.
>
> My only concerns are that it requires adjusting all existing usages of
> setUpTestData to assign to cls.data instead. It looks like it could be easy
> to forget doing so until you actually hit a data isolation issue. That
> makes setUpTestData unsafe to use unless you assign to data. That also
> creates two data "world" where objects assigned to cls and cls.data lose
> their references so altering self.data.book.author wouldn't affect
> self.author if the latter is not assigned to data.
>
> What about going through a deprecation period where non-picklable
> assignment during setUpTestData raises a deprecation warning suggesting
> using setUpClass or direct class attributes assignment? Another alternative
> could be to silently ignore deepcopy failures and return the original
> objects in these cases.
>
> Simon
>
> Le dimanche 25 novembre 2018 03:53:48 UTC-5, Adam Johnson a écrit :
>>
>> I have run into this problem myself in the past. On a previous project we
>> added a helper function to make deepcopy's of named attributes during
>> setUp().
>>
>> From a check against a few projects and Django's test suite[2] I have only
>>> identified a single issue which is that attributes assigned during
>>> `setUpTestData` would now have to be `deepcopy()`able but it shouldn't be
>>> a blocker given `Model` instance are.
>>
>>
>> I think this is too much of an ask for backwards compatibility. Lots of
>> things aren't deepcopy-able, as per its docs:
>>
>> This module does not copy types like module, method, stack trace, stack
>>> frame, file, socket, window, array, or any similar types. It does “copy”
>>> functions and classes (shallow and deeply), by returning the original
>>> object unchanged; this is compatible with the way these are treated by the
>>> pickle module.
>>
>>
>> How about adding a container object to TestCase, which deepcopy()'s its
>> attributes on setUp. It could be called something short like "data', which
>> would make your example:
>>
>> class BookTests(TestCase):
>>     @classmethod
>>     def setUpTestData(cls):
>>         cls.data.author = Author.objects.create()
>>         cls.data.book = cls.author.books.create()
>>
>>     def test_relationship_preserved(self):
>>         self.assertIs(self.data.book.author, self.data.author)
>>
>> On Sat, 24 Nov 2018 at 03:29, charettes <chare...@gmail.com> wrote:
>>
>>> Dear developers,
>>>
>>> Django 1.8 introduced the `TestCase.setUpTestData()` class method as a
>>> mean to
>>> speed up test fixtures initialization as compared to using `setUp()`[0].
>>>
>>> As I've come to use this feature and review changes from peers using it
>>> in
>>> different projects the fact that test data assigned during its execution
>>> couldn't be safely altered by test methods without compromising test
>>> isolation
>>> has often be the source of confusion and frustration.
>>>
>>> While the `setUpTestData` documentation mentions this limitation[1] and
>>> ways to
>>> work around it by using `refresh_from_db()` in `setUp()` I believe it
>>> defeats
>>> the whole purpose of the feature; avoiding unnecessary roundtrips to the
>>> database to speed up execution. Given `TestCase` goes through great
>>> lengths to
>>> ensure database level data isolation I believe it should do the same
>>> with class
>>> level in-memory data assigned during `setUpTestData`.
>>>
>>> In order to get rid of this caveat of the feature I'd like to propose an
>>> adjustment to ensure such in-memory test data isolation.
>>>
>>> What I suggest doing is wrapping all attributes assigned during
>>> `setUpTestData`
>>> in descriptors that lazily return `copy.deepcopy()`ed values on instance
>>> attribute accesses. By attaching the `deepcopy()`'s memo on test
>>> instances we
>>> can ensure that the reference graph between objects is preserved and thus
>>> backward compatible.
>>>
>>> In other words, the following test would pass even if `self.book` is a
>>> deep
>>> copy of `cls.book`.
>>>
>>> class BookTests(TestCase):
>>>     @classmethod
>>>     def setUpTestData(cls):
>>>         cls.author = Author.objects.create()
>>>         cls.book = cls.author.books.create()
>>>
>>>     def test_relationship_preserved(self):
>>>         self.assertIs(self.book.author, self.author)
>>>
>>> Lazily returning `deepcopy'ies and caching returned values in `__dict__`
>>> à la
>>> `cached_property` should also make sure the slight performance overhead
>>> this
>>> incurs is minimized.
>>>
>>> From a check against a few projects and Django's test suite[2] I have
>>> only
>>> identified a single issue which is that attributes assigned during
>>> `setUpTestData` would now have to be `deepcopy()`able but it shouldn't be
>>> a blocker given `Model` instance are.
>>>
>>> In order to allow other possible issues from being identified against
>>> existing
>>> projects I packaged the proposed feature[3] and made it available on
>>> pypi[4]. It
>>> requires decorating `setUpTestData` methods but it shouldn't be too hard
>>> to
>>> apply to your projects if you want to give it a try.
>>>
>>> Given this reaches consensus that this could be a great addition I'd file
>>> a ticket and finalize what I have so far[2].
>>>
>>> Thank your for your time,
>>> Simon
>>>
>>> [0]
>>> https://docs.djangoproject.com/en/1.8/releases/1.8/#testcase-data-setup
>>> [1]
>>> https://docs.djangoproject.com/en/2.1/topics/testing/tools/#django.test.TestCase.setUpTestData
>>> [2]
>>> https://github.com/charettes/django/compare/setuptestdata...charettes:testdata
>>> [3] https://github.com/charettes/django-testdata
>>> [4] https://pypi.org/project/django-testdata/
>>>
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>>
>>
>> --
>> Adam
>>
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-- 
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