'Construct the switch_collection context manager.
:param cls: the class to change the registered db
:param collection_name: the name of the collection to use'

def __init__(self, cls, collection_name):

    self.cls = cls
    self.ori_collection = cls._get_collection()
    self.ori_get_collection_name = cls._get_collection_name
    self.collection_name = collection_name
