Propagating fixtures to test class attribute

Hi there.

I’d like to share my thought about using fixture in tests classes and maybe ask some advise. Current issue is related to two useful methods for newcomers from setuptools: (mark.usefixture and autouse - option for fixture) and using this stuff in Test classes.

First thing - (mark.usefixture) allows to define fixtures fro whole test class, but it does not provide ability to get access to this fixture from the test. For this purposes I have to define fixtures as parameters of test methods, like:

class TestExample():                  
    def test_one(self, param):               
        param.return_value = 100

honestly it’s not a big deal, when you have couple of the test. However for huge numbers of the test, where I have the same fixtures, I’d like to hide avoid using fixture parameter. So I have to do it in the such way:

class TestExample():                  
   @pytest.fixture(autouse=True)    
    def init_fixture(param1, param2):
        self.param1 = param1         
        self.param2 = param2         

    def test_one(self):               
        self.param1.return_value = 100
        self.param2.return_value = 200

So the main idea -to hide explicitly mentioned fixtures of the function and providing them as class attribute. It’s also can be useful, when you port some test from testscenario extension, where parameters are available as class attributes.

I suppose, that it can be done by improving “mark.usefixtures” decorator, where it allows to add fixtures as class attributes. So potentially decorator can have syntax, like: mark.usefixtures(*args, as_attrs=False), where *args - is list of fixtures, as previously and as_attrs is a flag (defailt is False), which save fixtures as class attributes. In case if function has not class it may be ignored or raise warning message.

Finally I suppose, that it can be done by adding minimal logic here: https://github.com/pytest-dev/pytest/blob/master/_pytest/python.py#L143

def pytest_pyfunc_call(pyfuncitem):                 
    testfunction = pyfuncitem.obj                   
+   if pyfuncitem.cls:
+         for k, v in pyfuncitem.funcargs:
+             setattr(pyfuncitem.cls, k, v) 
    if pyfuncitem._isyieldedfunction():             
        testfunction(*pyfuncitem._args)             
    else:                                           
        funcargs = pyfuncitem.funcargs              
        testargs = {}                               
        for arg in pyfuncitem._fixtureinfo.argnames:
            testargs[arg] = funcargs[arg]           
        testfunction(**testargs)                    
    return True        

Please correct me if I wrong somewhere or share your opinion about such change in the project.

[nicoddemus]

@skraynev great, glad it worked out.

Can I persuade you to write a short post about this to the pytest-tricks blog? 😉

cc @hackebrot

[nicoddemus]

yes, imho a explicit class level fixture that sets the attribute is waaaaay more transparent and already supported directly without anyhacks

Indeed it might be better to support this using something else other than pytest.mark.usefixtures, I don’t know for certain until we see some working code though.

But not sure how much more transparent using something else other than pytest.mark.usefixtures would be, to be honest.

Instead of:

@pytest.mark.usefixtures('tmpdir', 'foobar', as_attrs=True)
class Test:
    ...

It would be some other construct at the class level anyway, perhaps:

@pytest.fixtures_as_attrs('tmpdir', 'foobar')
class Test:
    ...

Why would be the first be more transparent than the second, from a user’s point of view?

Unless your point is that using marks for this would be problematic from an implementation POV, but that’s a different discussion.

from my pov usefixtures is a unfortunate hack and we should completely remove the need to have it

I’m curious, was @pytest.mark.usefixtures added with the intent of making it easy for groups of tests to “auto use” fixtures without declaring them explicitly? Because for a single test case I don’t see much value in mark.usefixtures as you can just declare that parameter there, but for marking tests in classes and modules it makes more sense. Just curious because I don’t know pytest for so long. 😁