[pytest-dev] Fixture ordering and scopes

[Isaul Vargas]

Another reason in support of a well defined order is because some library
authors will create function scoped fixtures that depend on the objects in
a session scoped fixture. If those tests do run out of order, tests will
break.


On Fri, Mar 16, 2018 at 8:18 AM, Vasily Kuznetsov <kvas.it at gmail.com> wrote:

> Hi Bruno,
>
> Your example is a good argument, I haven't considered third party fixtures
> over which the developer of the test suite has less control. I agree that
> requiring users to jumps through extra hoops to give third-party fixtures
> the desired order is too high of a price to pay for the nudge towards good
> style (explicitly declaring dependencies) that we get from undefined order.
>
> Once we decide to give some guarantees about the order of fixture
> execution your new approach certainly makes sense.
>
> Cheers,
> Vasily
>
>
> On Fri, Mar 16, 2018 at 12:34 PM Bruno Oliveira <nicoddemus at gmail.com>
> wrote:
>
>> Hi Vasily!
>>
>> On Fri, Mar 16, 2018 at 7:17 AM Vasily Kuznetsov <kvas.it at gmail.com>
>> wrote:
>>
>>> I very much agree with Floris that if you need fixture A to run before
>>> fixture B and otherwise things break, this is called "dependency" and it's
>>> better if it's explicitly declared.
>>>
>>
>> Definitely, if a fixture requires something that is done by another
>> fixture, then that dependency should be explicitly defined; but the issue
>> is more that people expect higher level scoped fixtures to be executed
>> first, and when you mix autouse fixtures and usefixtures markers, the order
>> is non-intuitive.
>>
>>
>>
>>> I can't easily imagine a situation where declaring dependencies would be
>>> too much work or not desirable for some other reason but maybe it's just my
>>> imagination not being good enough :).
>>>
>>
>> I wrote an example which demonstrates this in a separate reply to Floris.
>>
>> Outer scopes running before inner scopes does sound kind of logical but
>>> everything running lazily on demand (as it does now) also makes sense.
>>>
>>
>> Just to be clear, in my PR fixtures are still created lazily, it is just
>> that we sort them by scope (preserving order) first.
>>
>> Cheers,
>> Bruno.
>>
>
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