使用闭包创建Python类方法

Question

我第一次使用unittest模块（因为我对Python很陌生），我发现自己一遍又一遍地执行相同的测试断言。我想将该代码拉出到一个公共函数中，但unittest断言是TestCase的方法（即self.assertTrue）。我尝试使用闭包来构造每个TestCase中为我执行断言的类方法。例如：

def _keys_in_dict_asserter(cls):
    """
    A simple closure that creates an "assert keys in dict" function for each TestCase
    """

    def cls_asserter(dictionary, *args):

        for key in args:
           cls.assertTrue(key in dictionary)

    return cls_asserter

class TestFunctionUnderTest(TestCase):

    # I want to create an asserter function as a class method using this
    # class object. Python won't let me. Why?
    @classmethod   
    keys_in_dict = _keys_in_dict_asserter(cls)  

    def test_returned_dict_contains_expected_items(self):
        """
        Make sure the dict returned has all the keys expected by the caller under normal operation
        """

        keys_in_dict(function_under_test())

但是，我不确定如何正确地写这个。帮助