Question

I’ve been working on a way to get tests produced from a generator in nose to have descriptions that are customized for the specific iteration being tested. I have something that works, as long as my generator target method never tries to access self from my generator class. I’m seeing that all my generator target instances have a common test class instance while nose is generating a one-offed instance of the test class for each test run from the generator. This is resulting in setUp being run on each test instance nose creates, but never running on the instance the generator target is bound to (of course, the real problem is that I can’t see how to bind the nose-created instance to the generator target). Here’s the code I’m using to try to figure this all out (yes, I know the decorator would probably be better as a callable class, but nose, at least version 1.2.1 that I have, explicitly checks that tests are either functions or methods, so a callable class won’t run at all):

import inspect

def labelable_yielded_case(case):

    argspec = inspect.getargspec(case)
    if argspec.defaults is not None:
        defaults_list = [''] * (len(argspec.args) - len(argspec.defaults)) + argspec.defaults
    else:
        defaults_list = [''] * len(argspec.args)
    argument_defaults_list = zip(argspec.args, defaults_list)
    case_wrappers = []

    def add_description(wrapper_id, argument_dict):

        case_wrappers[wrapper_id].description = case.__doc__.format(**argument_dict)

    def case_factory(*factory_args, **factory_kwargs):

        def case_wrapper_wrapper():

            wrapper_id = len(case_wrappers)

            def case_wrapper(*args, **kwargs):

                args = factory_args + args
                argument_list = []
                for argument in argument_defaults_list:
                    argument_list.append(list(argument))
                for index, value in enumerate(args):
                    argument_list[index][1] = value
                argument_dict = dict(argument_list)
                argument_dict.update(factory_kwargs)
                argument_dict.update(kwargs)
                add_description(wrapper_id, argument_dict)
                return case(*args, **kwargs)

            case_wrappers.append(case_wrapper)
            case_wrapper.__name__ = case.__name__
            return case_wrapper

        return case_wrapper_wrapper()

    return case_factory


class TestTest(object):

    def __init__(self):

        self.data = None

    def setUp(self):

        print 'setup', self
        self.data = (1,2,3)

    def test_all(self):

        for index, value in enumerate((1,2,3)):
            yield self.validate_equality(), index, value

    def test_all_again(self):

        for index, value in enumerate((1,2,3)):
            yield self.validate_equality_again, index, value

    @labelable_yielded_case
    def validate_equality(self, index, value):
        '''element {index} equals {value}'''

        print 'test', self
        assert self.data[index] == value, 'expected %d got %d' % (value, self.data[index])

    def validate_equality_again(self, index, value):

        print 'test', self
        assert self.data[index] == value, 'expected %d got %d' % (value, self.data[index])

    validate_equality_again.description = 'again'

When run through nose, the again tests work just fine, but the set of tests using the decorated generator target all fail because self.data is None (because setUp is never run because the instance of TestTest stored in the closures is not the instances run by nose). I tried making the decorator an instance member of a base class for TestTest, but then nose threw errors about having too few arguments (no self) passed to the unbound labelable_yielded_case. Is there any way I can make this work (short of hacking nose), or am I stuck choosing between either not being able to have the yield target be an instance member or not having per-test labeling for each yielded test?

Answer 1

Fixed it (at least for the case here, though I think I got it for all cases). I had to fiddle with case_wrapper_wrapper and case_wrapper to get the factory to return the wrapped cases attached to the correct class, but not bound to any given instance in any way. I also had another code issue because I was building the argument dict in wrapper wrapper, but then not passing it to the case. Working code:

import inspect

def labelable_yielded_case(case):

    argspec = inspect.getargspec(case)
    if argspec.defaults is not None:
        defaults_list = [''] * (len(argspec.args) - len(argspec.defaults)) + argspec.defaults
    else:
        defaults_list = [''] * len(argspec.args)
    argument_defaults_list = zip(argspec.args, defaults_list)
    case_wrappers = []

    def add_description(wrapper_id, argument_dict):

        case_wrappers[wrapper_id].description = case.__doc__.format(**argument_dict)

    def case_factory(*factory_args, **factory_kwargs):

        def case_wrapper_wrapper():

            wrapper_id = len(case_wrappers)

            def case_wrapper(*args, **kwargs):

                argument_list = []
                for argument in argument_defaults_list:
                    argument_list.append(list(argument))
                for index, value in enumerate(args):
                    argument_list[index][1] = value
                argument_dict = dict(argument_list)
                argument_dict.update(kwargs)
                add_description(wrapper_id, argument_dict)
                return case(**argument_dict)

            case_wrappers.append(case_wrapper)
            case_name = case.__name__ + str(wrapper_id)
            case_wrapper.__name__ = case_name
            if factory_args:
                setattr(factory_args[0].__class__, case_name, case_wrapper)
                return getattr(factory_args[0].__class__, case_name)
            else:
                return case_wrapper

        return case_wrapper_wrapper()

    return case_factory


class TestTest(object):

    def __init__(self):

        self.data = None

    def setUp(self):

        self.data = (1,2,3)

    def test_all(self):

        for index, value in enumerate((1,2,3)):
            yield self.validate_equality(), index, value

    @labelable_yielded_case
    def validate_equality(self, index, value):
        '''element {index} equals {value}'''

        assert self.data[index] == value, 'expected %d got %d' % (value, self.data[index])