def register_sizer(self, attr_name, sizedimage_cls):
        if attr_name.startswith(
            '_'
        ) or attr_name in self.unallowed_sizer_names:
            raise UnallowedSizerName(
                "`%s` is an unallowed Sizer name. Sizer names cannot begin "
                "with an underscore or be named any of the "
                "following: %s." % (
                    attr_name,
                    ', '.join([
                        name
                        for name in self.unallowed_sizer_names
                    ])
                )
            )
        if not issubclass(sizedimage_cls, SizedImage):
            raise InvalidSizedImageSubclass(
                'Only subclasses of versatileimagefield.datastructures.'
                'SizedImage may be registered with register_sizer'
            )

        if attr_name in self._sizedimage_registry:
            raise AlreadyRegistered(
                'A SizedImage class is already registered to the `%s` '
                'attribute. If you would like to override this attribute, '
                'use the unregister method' % attr_name
            )
        else:
            self._sizedimage_registry[attr_name] = sizedimage_cls
Test if it List all users in detail
dataset/ETHPy150Open WGBH/django-versatileimagefield/versatileimagefield/registry.py/VersatileImageFieldRegistry.register_sizer--crossover with--dataset/ETHPy150Open saltstack/salt/tests/unit/modules/ilo_test.py/IloTestCase.test_list_users_info