def METHOD_NAME(self):
    class MyBase:
        def __init__(self):
            self.extensions = []
        def add_extension(self, ext_item):
            self.extensions.append(ext_item)
    @extend(MyBase, 'my_ext_1', inst_handler='add_extension')
    class MyExt1:
        def __init__(self, base: MyBase):
            pass
    @extend(MyBase, 'my_ext_2', inst_handler='add_extension')
    class MyExt2:
        def __init__(self, base: MyBase):
            pass
    my_base = MyBase()
    self.assertEqual([],
                     my_base.extensions)
    self.assertIsInstance(my_base.my_ext_1, MyExt1)
    self.assertIsInstance(my_base.my_ext_2, MyExt2)
    self.assertEqual(2,
                     len(my_base.extensions))