'Parse `xml` as an XBlock, and add it to `self._descriptors`'

def process_xml(self, xml):

    self.get_asides = Mock(return_value=[])
    descriptor = self.xblock_from_node(etree.fromstring(xml), None, CourseLocationManager(self.course_id))
    self._descriptors[descriptor.location.to_deprecated_string()] = descriptor
    return descriptor
