[pytest-dev] Fixture ordering and scopes

[Isaul Vargas]

I too have observed this weird ordering. I would like like the order of
fixtures to always respect the order of scopes.

On Thu, Mar 15, 2018 at 6:47 PM, Brian Okken <variedthoughts at gmail.com>
wrote:

> Bruno,
>
> Please, merge that PR!
> caveat: I have not reviewed the code.
>
> However, ...
> I get numerous questions about it, and I always tell people to create
> artificial dependencies between fixtures that need to run in a certain
> order.
> The general mental model that people have for fixtures is that they are
> run in scope order.
> I think the current behavior of file order overriding scope order is
> insane and a bug.
>
> - Brian
>
> On Thu, Mar 15, 2018 at 2:42 PM, Bruno Oliveira <nicoddemus at gmail.com>
> wrote:
>
>> Hi everyone and Holger,
>>
>> Looking at the code below:
>>
>>
>> data = {}
>> @pytest.fixture(scope='session')def clean_data():
>>     data.clear()
>> @pytest.fixture(autouse=True)def add_data():
>>     data['value'] = 1
>> @pytest.mark.usefixtures('clean_data')def test_foo():
>>     assert data.get('value')
>>
>> Should test_foo fail or pass? Keep your answer in mind before
>> proceeding. :)
>> ------------------------------
>>
>> I ask this because *unrelated* fixtures, i.e. which don’t depend on each
>> other, are executed in the order they are declared in the test function
>> signature, regardless of scope.
>>
>> The example above *fails*, because the fixtures are executed in (add_data,
>> clean_data) order: add_data, being *autouse*, is added to the beginning
>> of the argument list, and afterwards clean_data is inserted because of
>> the usefixtures mark.
>>
>> This came up in #2405 <https://github.com/pytest-dev/pytest/issues/2405>,
>> where Jason Coombs assumed that clean_data, being session-scoped, would
>> always be executed first.
>>
>> I wonder if the current state of things is by design, or just an accident
>> of how things work?
>>
>> I opened up a PR <https://github.com/pytest-dev/pytest/pull/3306> which
>> does sort parameters by scope while keeping the relative order of fixtures
>> of same scope intact, and the test suite passes without failures so if the
>> current behavior is by design there are not tests enforcing it. Using code
>> in the PR, then things might also be surprising:
>>
>> @pytest.fixture(scope='session')def s(): pass
>> @pytest.fixture(scope='function')def f(): pass
>> def test_foo(f, s):
>>     pass
>>
>> s and f are unrelated and execute in (f, s) order in master, but in (s,
>> f) order in my branch.
>>
>> Would like to hear what people think about this matter, as I think it is
>> an important one, specially *Holger* if this is a design decision or
>> just an accident of implementation, and if we should change it.
>>
>> Also, please feel free to just reply with what you thought what should be
>> the behavior of the first sample.
>>
>> Cheers,
>> Bruno.
>> ​
>>
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>>
>
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