[TIP] Modifying fixture parametrization from the command line

[Laurent Brack]

Hi Holger,

On 10/29/14, 10:31 AM, holger krekel wrote:
> Hi Laurent,
>
> On Wed, Oct 29, 2014 at 09:22 -0700, Laurent Brack wrote:
>> Hi,
>>
>> I have been struggling with this issue and couldn't find a way to
>> make it work.
>>
>> For sake of simplicity, say I take in the example from the documentation
>>
>> http://pytest.org/latest/fixture.html#parametrizing-a-fixture
>>
>> but want to give the user the ability, to change the list of mail
>> servers from the command line (say smtp.gmail.com).
>
> You can't do this through direct fixture parametrization.  But there
> is a hook you can easily use, pytest_generate_tests.  Here is a full
> example probably fitting quite exactly your use case:
>
> http://pytest.org/latest/parametrize.html#basic-pytest-generate-tests-example

Thanks. I use this hook for other things and when I saw the email from 
Wouter this morning I was thinking of doing this, however ...

The advantage of using fixtures is that if say reaching smpt.gmail.com 
fails, the tests depending on that fixture would be marked as error 
which is what you want (in our case, we use devices) but I am not sure 
what I can do in pytest_generate_tests. Throwing an exception is not 
want you want to do off course, and ignoring the faulty device would 
lead to the test not showing up at all in the report (makes sense?).

>
> Pity there is no searchable pytest cookbook yet so you could have found
> this more easily.
Here is an idea for a book :)
>
> HTH,
It does, it confirms this can't be done via fixtures ... at least not in 
the conventional way :)
> holger
>
best/Laurent
>
>> Basically
>>
>> @pytest.fixture(scope="module",
>>                  params=["merlinux.eu", "mail.python.org"])
>> def smtp(request):
>>      smtp = smtplib.SMTP(request.param)
>>      ...
>>
>> becomes
>>
>> @pytest.fixture(scope="module",
>>                  params=["smtp.gmail.com"])
>> def smtp(request):
>>     ...
>>
>> At runtime.
>>
>> The problem I had is that list given in "params" is created when
>> conftest is loaded which is before the pytest_addoption and
>> pytest_configure are invoked.
>>
>> I tried to use a global variable (yuk) and modify the list content
>> in the hook hoping that the fixture keeps the same reference but
>> this didn't work.
>>
>> Is there anyway I can do this?
>>
>> Thanks in advance.
>>
>> /Laurent
>>
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