def METHOD_NAME(self):
    class MyBase:
        extensions = []
        @classmethod
        def add_extension(cls, ext_item):
            MyBase.extensions.append(ext_item)
    @extend(MyBase, 'my_ext_1', class_handler='add_extension')
    class MyExt1:
        def __init__(self, base: MyBase):
            pass
    @extend(MyBase, 'my_ext_2', class_handler='add_extension')
    class MyExt2:
        def __init__(self, base: MyBase):
            pass
    self.assertEqual([('my_ext_1', MyExt1),
                      ('my_ext_2', MyExt2)],
                     MyBase.extensions)