谁能告诉我为什么这行不通?
>>> import mock
>>> @mock.patch('datetime.date.today')
... def today(cls):
... return date(2010, 1, 1)
...
>>> from datetime import date
>>> date.today()
datetime.date(2010, 12, 19)
也许有人能提出一个更好的办法?
谁能告诉我为什么这行不通?
>>> import mock
>>> @mock.patch('datetime.date.today')
... def today(cls):
... return date(2010, 1, 1)
...
>>> from datetime import date
>>> date.today()
datetime.date(2010, 12, 19)
也许有人能提出一个更好的办法?
当前回答
http://blog.xelnor.net/python-mocking-datetime/中讨论了几种解决方案。总而言之:
模拟对象-简单有效,但打破isinstance()检查:
target = datetime.datetime(2009, 1, 1)
with mock.patch.object(datetime, 'datetime', mock.Mock(wraps=datetime.datetime)) as patched:
patched.now.return_value = target
print(datetime.datetime.now())
模拟类
import datetime
import mock
real_datetime_class = datetime.datetime
def mock_datetime_now(target, dt):
class DatetimeSubclassMeta(type):
@classmethod
def __instancecheck__(mcs, obj):
return isinstance(obj, real_datetime_class)
class BaseMockedDatetime(real_datetime_class):
@classmethod
def now(cls, tz=None):
return target.replace(tzinfo=tz)
@classmethod
def utcnow(cls):
return target
# Python2 & Python3 compatible metaclass
MockedDatetime = DatetimeSubclassMeta('datetime', (BaseMockedDatetime,), {})
return mock.patch.object(dt, 'datetime', MockedDatetime)
使用:
with mock_datetime_now(target, datetime):
....
其他回答
对于那些在测试类中使用补丁程序的人,下面是我如何成功地修补datetime功能:
from datetime import datetime
import unittest
from unittest.mock import Mock, patch
# Replace with the proper path to the module you would
# like datetime to be mocked
from path.to.my_module
class MyTestCases(unittest.TestCase):
def setUp(self):
"""execute on class instantiation"""
# Record both times at the same moment
self.dt_now, self.dt_utcnow = datetime.now(), datetime.utcnow()
# After retrieving real (or hardcoded datetime values),
# proceed to mock them in desired module
self.patch_datetime_functions()
def patch_datetime_functions(self) -> None:
"""
Patch datetime.now() and datetime.utcnow() to prevent issues when
comparing expected dates
"""
# Create a patcher
self.patcher_dt = patch(
'path.to.my_module'
)
# Start but make sure cleanup always occurs
self.patcher_dt.start()
self.addCleanup(self.patcher_dt.stop)
# Perform the actual patch – use lambdas as mock functions
datetime_mock = Mock(wraps=datetime)
datetime_mock.now.return_value = self.dt_now
datetime_mock.utcnow.return_value = self.dt_utcnow
my_module.datetime = datetime_mock
# Here's what it will look like when testing:
def some_test(self):
curr_dt = self.dt_now
returned_dt = my_module.datetime.utcnow()
# Compare the dates
self.assertEqual(curr_dt, returned_dt,
'Datetime values should be equal'
)
一般来说,你会有datetime或datetime。将日期导入某个模块。模拟该方法的一种更有效的方法是在导入它的模块上修补它。例子:
a.py
from datetime import date
def my_method():
return date.today()
然后,对于您的测试,模拟对象本身将作为参数传递给测试方法。您将使用所需的结果值设置模拟,然后调用测试中的方法。然后您可以断言您的方法完成了您想要的。
>>> import mock
>>> import a
>>> @mock.patch('a.date')
... def test_my_method(date_mock):
... date_mock.today.return_value = mock.sentinel.today
... result = a.my_method()
... print result
... date_mock.today.assert_called_once_with()
... assert mock.sentinel.today == result
...
>>> test_my_method()
sentinel.today
警告一句。很有可能嘲讽得过火了。当您这样做时,它会使您的测试更长、更难理解,并且不可能维护。在模拟像datetime.date这样简单的方法之前。今天,问问自己是否真的需要嘲笑它。如果您的测试短小精干,并且在不模拟函数的情况下运行良好,那么您可能只看到了正在测试的代码的内部细节,而不是需要模拟的对象。
在Daniel G的解决方案中补充一点:
from datetime import date
class FakeDate(date):
"A manipulable date replacement"
def __new__(cls, *args, **kwargs):
return date.__new__(date, *args, **kwargs)
这将创建一个类,当实例化时,该类将返回一个正常的datetime。对象,但也可以更改。
@mock.patch('datetime.date', FakeDate)
def test():
from datetime import date
FakeDate.today = classmethod(lambda cls: date(2010, 1, 1))
return date.today()
test() # datetime.date(2010, 1, 1)
下面是另一种模拟datetime.date.today()的方法,其额外的好处是其余的datetime函数继续工作,因为模拟对象被配置为包装原始的datetime模块:
from unittest import mock, TestCase
import foo_module
class FooTest(TestCase):
@mock.patch(f'{foo_module.__name__}.datetime', wraps=datetime)
def test_something(self, mock_datetime):
# mock only datetime.date.today()
mock_datetime.date.today.return_value = datetime.date(2019, 3, 15)
# other calls to datetime functions will be forwarded to original datetime
注意mock.patch()的wraps=datetime参数——当foo_module使用date.today()之外的其他datetime函数时,它们将被转发到原始包装的datetime模块。
值得注意的是,Mock文档专门讨论了datetime.date.today,并且可以在不创建虚拟类的情况下做到这一点:
https://docs.python.org/3/library/unittest.mock-examples.html#partial-mocking
>>> from datetime import date
>>> with patch('mymodule.date') as mock_date:
... mock_date.today.return_value = date(2010, 10, 8)
... mock_date.side_effect = lambda *args, **kw: date(*args, **kw)
...
... assert mymodule.date.today() == date(2010, 10, 8)
... assert mymodule.date(2009, 6, 8) == date(2009, 6, 8)
...