此脚本失败：
import mock
class MyClass(object):
@classmethod
def my_method(cls):
print('my_method')
def mocked_method(cls):
print('I want this method to get called')
with mock.patch.object(MyClass,'my_method',mocked_method):
MyClass.my_method()
例外：
Traceback (most recent call last):
File "/home/foo/tmp/test_mocking_classmethod.py",line 14,in <module>
MyClass.my_method()
TypeError: unbound method mocked_method() must be called with MyClass instance as first argument (got nothing instead)
解决方法
Python函数是
descriptors,Python将这些函数绑定到它们被查找的实例,或者在classmethod的情况下,绑定到类.因为你没有在替换函数上使用classmethod装饰器,所以它被错误地绑定(作为常规方法,因此没有传入cls).
只需手动将目标包装在classmethod装饰器中：
with mock.patch.object(MyClass,classmethod(mocked_method)):
MyClass.my_method()
这里我手动应用了@classmethod装饰器,但您也可以直接在目标函数上使用它作为装饰器：
@classmethod
def mocked_method(cls):
print('I want this method to get called')
with mock.patch.object(MyClass,mocked_method):
MyClass.my_method()
演示：
>>> import mock
>>> class MyClass(object):
... @classmethod
... def my_method(cls):
... print('my_method')
...
>>> def mocked_method(cls):
... print('I want this method to get called')
...
>>> with mock.patch.object(MyClass,classmethod(mocked_method)):
... MyClass.my_method()
...
I want this method to get called