Python 上的不同 unittest.mock 行为 2/3

Question

I have the unittest that should be compatible with both python 2 and 3. It looks like that:

def test_getModulePath_BuildInThrowsAnException(self):
    resource = mock.Mock(spec=some.module.SomeClass)
    resource.name = 'BuiltIn'
    resource.parent = resource

    if sys.version_info[0] == 3:  # Python 3
        patched_class = '_frozen_importlib_external.SourceFileLoader'
    else:  # Python 2
        patched_class = 'pkgutil.ImpLoader'

    with mock.patch(patched_class) as loader_mock:
        loader_mock.side_effect = MyException
        try:
            result = MyClass._get_module_path(resource)
            self.assertIsNone(result)
        except MyException as e:
            self.fail(e)

The method i want to test:

@classmethod
def _get_module_path(cls, resource):
    ...
    try:
        loader = pkgutil.get_loader(resource.name)
    except MyException as e:
        return None
    ...
    return loader.get_filename() 

The problem is that pkgutil.get_loader() returnes different objects which depends on python version. On Py2 everything is ok, loader raises an error as side_effect, method returnes None and loader_mock.called = True . But on Py3 loader side_effect doesn't work and method goes to return loader.gt_filename() . Any ideas? Python version: 2.7.15 and 3.6.3

Answer 1

I think, the problem is related with python import system, because the object returned by get_loader is exectly a _frozen_importlib_external.SourceFileLoader , but side_effect is not raised. The problem was solved by patching pkgutil.get_loader function, not the return object class:

        with mock.patch('pkgutil.get_loader', side_effect=MyException):
            try:
                result = MyClass._get_module_path(resource)
                self.assertIsNone(result)
            except MyException as e:
                self.fail(e)

I hope this will help someone. Thanks.