python - 模拟接受 **kwargs 的函数

Question

我在模拟接受 **kwargs 的函数时遇到问题。场景是我有 ClassA (在我的具体情况下是我没有写的)并且它有一个带有 **kwargs 的函数。 ClassB 具有 ClassA 的实例，并调用 **kwargs 函数。我想通过模拟对 A 类函数的调用来测试 ClassB。

这是我到目前为止所尝试过的，在我的两次尝试中我都以类型错误告终。有什么办法可以做到这一点吗？我应该重新考虑这个问题的另一个方面吗？

import unittest


#a class i have no control over. Has a function accepting **kwargs
class ClassA(object):

    def classFunctionAcceptingKwargs(self, **kwargs):
        return kwargs["a"] + kwargs["b"]

# a mock of the above class
class Mock_ClassA(object):

    def __init__(self):
        self.mockclassFunctionAcceptingKwargs = lambda **kwargs: None

    def classFunctionAcceptingKwargs(self, **kwargs):
        #FAILS: TypeError: mockFunctionAcceptingKwargs() takes exactly 0 arguments (1 given)
        return self.mockclassFunctionAcceptingKwargs(kwargs)
        #ALSO FAILS: TypeError: mockFunctionAcceptingKwargs() argument after ** must be a mapping, not set
        #return self.mockclassFunctionAcceptingKwargs(**{kwargs["a"] + kwargs["b"]})

#class B calls the class A kwargs but exposes a function with a dict
class ClassB(object):
    def __init__(self, classA):
        self.classA = classA

    def doSomething(self, dict):
        return self.classA.classFunctionAcceptingKwargs(**dict)

class TestClassA(unittest.TestCase):

    def runTest(self):
        a = ClassA()
        result = a.classFunctionAcceptingKwargs(**{"a":1, "b": 2})
        self.assertEqual(result, 3)

class TestClassB(unittest.TestCase):

    def runTest(self):

        mock = Mock_ClassA()
        def mockFunctionAcceptingKwargs(**kwargs):
            self.assertEqual(kwargs["a"], 1)
            self.assertEqual(kwargs["b"], 2)

        mock.mockclassFunctionAcceptingKwargs = mockFunctionAcceptingKwargs
        b = ClassB(mock)
        b.doSomething({"a": 1, "b": 2})

堆栈跟踪:

Test Name:  TestClassB
Test Outcome:   Failed
Result StandardError:   
======================================================================
ERROR: runTest (module1.TestClassB)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\test\module1.py", line 49, in runTest
    b.doSomething({"a": 1, "b": 2})
  File "C:\test\module1.py", line 28, in doSomething
    return self.classA.classFunctionAcceptingKwargs(**dict)
  File "C:\test\module1.py", line 18, in classFunctionAcceptingKwargs
    return self.mockclassFunctionAcceptingKwargs(kwargs)
TypeError: mockFunctionAcceptingKwargs() takes exactly 0 arguments (1 given)
----------------------------------------------------------------------
Ran 1 test in 12.873s
FAILED (errors=1)

Answer 1

我不确定你为什么要调用另一个函数。但是，如果您必须有一个实例属性mockclassFunctionAcceptingKwargs函数，那么只需使用**kwargs传递kwargs字典即可:

class Mock_ClassA(object):
    # ...
    def classFunctionAcceptingKwargs(self, **kwargs):
        return self.mockclassFunctionAcceptingKwargs(**kwargs)

如果您只需要 classFunctionAcceptingKwargs 存在，则根本不需要调用该 lambda:

class Mock_ClassA(object):
    def __init__(self, mock_result):
        self.mock_result = mock_result
    def classFunctionAcceptingKwargs(self, **kwargs):
        self.called_with = kwargs
        return self.mock_result

然后只需传递模拟的返回值，无论您需要传递回 ClassB 进行测试，然后您都可以检查是否也传递了正确的值:

mock = Mock_ClassA(3)  # to return 3 back to the caller
b = ClassB(mock)
b.doSomething({"a": 1, "b": 2})
self.assertEqual(mock.called_with, {'a': 1, 'b': 2})

您可能想使用unittest.mock library构建要传入的模拟对象(在 Python 3 中可用，并且可以安装适用于 Python 2 的 backport)。它可以让您创建一个模拟的 ClassA，然后使用 API 来测试该模拟是否按预期方式使用:

try:
    # Python 3
    from unittest import mock
except ImportError:
    # Python 2, backport
    import mock

class TestClassB(unittest.TestCase):
    def runTest(self):
        mockA = mock.Mock(spec=ClassA)  # only accept attributes ClassA also has
        mockA.classFunctionAcceptingKwargs.return_value = 3  # or whatever else you want it to return
        b = ClassB(mockA)
        b.doSomething({"a": 1, "b": 2})
        mockA.classFunctionAcceptingKwargs.assert_called_once_with(a=1, b=2)

使用 unittest.mock 作为模拟层的演示:

>>> from unittest import mock
>>> class ClassA(object):
...     def classFunctionAcceptingKwargs(self, **kwargs):
...         return kwargs["a"] + kwargs["b"]
...
>>> class ClassB(object):
...     def __init__(self, classA):
...         self.classA = classA
...     def doSomething(self, dict):
...         return self.classA.classFunctionAcceptingKwargs(**dict)
...
>>> mockA = mock.Mock(spec=ClassA)
>>> mockA.classFunctionAcceptingKwargs.return_value = 3
>>> b = ClassB(mockA)
>>> b.doSomething({"a": 1, "b": 2})
3
>>> mockA.classFunctionAcceptingKwargs.assert_called_once_with(a=1, b=2)  # passes, no exception raised
>>> mockA.mock_calls
[call.classFunctionAcceptingKwargs(a=1, b=2)]