python - 模拟一个类方法并将 self 参数传递给 Mock 的副作用
问题描述
我正在尝试在单元测试中修补现有类中的单个方法。要修补的类是:
class Example:
def __init__(self: "Example", id: int) -> None:
self.id : int = id
self._loaded : bool = False
self._data : typing.Union[str,None] = None
def data(self: "Example") -> str:
if not self._loaded:
self.load()
return self._data
def load(self: "Example") -> None:
self._loaded = True
# some expensive computations
self._data = f"real_data{self.id}"
因此,不是调用self.load()
a而是unittest.mock.Mock
使用mocked_load
函数(如下)作为副作用调用:
def mocked_load(self: "Example") -> None:
# mock the side effects of load without the expensive computation.
self._loaded = True
self._data = f"test_data{self.id}"
第一次尝试是:
@unittest.mock.patch.object(Example, "load", new = mocked_load)
def test_data__patch_new(
self: "TestExample",
) -> None:
example1 = Example(id=1)
example2 = Example(id=2)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
这可行,但只是用Example.load
函数替换函数,mocked_load
而不是将其包装在Mock
; 所以,虽然它确实通过了,但你不能扩展测试来断言修补Example.load
方法被调用了多少次。这不是我正在寻找的解决方案。
第二次尝试是:
@unittest.mock.patch.object(Example, "load")
def test_data__patch_side_effect(
self: "TestExample",
patched_load: unittest.mock.Mock
) -> None:
patched_load.side_effect = mocked_load
example1 = Example(id=1)
example2 = Example(id=2)
self.assertEqual(patched_load.call_count, 0)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
self.assertEqual(patched_load.call_count, 1)
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
self.assertEqual(patched_load.call_count, 2)
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
self.assertEqual(patched_load.call_count, 2)
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
self.assertEqual(patched_load.call_count, 2)
这失败了,但有以下例外:
Traceback (most recent call last):
File "/usr/lib/python3.8/unittest/mock.py", line 1325, in patched
return func(*newargs, **newkeywargs)
File "my_file.py", line 65, in test_data__patch_side_effect
data1_1 = example1.data()
File "my_file.py", line 13, in data
self.load()
File "/usr/lib/python3.8/unittest/mock.py", line 1081, in __call__
return self._mock_call(*args, **kwargs)
File "/usr/lib/python3.8/unittest/mock.py", line 1085, in _mock_call
return self._execute_mock_call(*args, **kwargs)
File "/usr/lib/python3.8/unittest/mock.py", line 1146, in _execute_mock_call
result = effect(*args, **kwargs)
TypeError: mocked_load() missing 1 required positional argument: 'self'
最后的尝试是:
@unittest.mock.patch.object(Example, "load")
def test_data__patch_multiple_side_effect(
self: "TestExample",
patched_load: unittest.mock.Mock
) -> None:
example1 = Example(id=1)
example2 = Example(id=2)
side_effect1 = lambda: mocked_load( example1 )
side_effect2 = lambda: mocked_load( example2 )
patched_load.side_effect = side_effect1
self.assertEqual(patched_load.call_count, 0)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
self.assertEqual(patched_load.call_count, 1)
patched_load.side_effect = side_effect2
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
self.assertEqual(patched_load.call_count, 2)
patched_load.side_effect = side_effect1
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
self.assertEqual(patched_load.call_count, 2)
patched_load.side_effect = side_effect2
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
self.assertEqual(patched_load.call_count, 2)
这“有效”但它非常脆弱,因为self
参数被硬编码到函数中,并且需要交换lambda
模拟以匹配每个调用。side_effect
完整的最小代表性示例是:
import typing
import unittest
import unittest.mock
class Example:
def __init__(self: "Example", id: int) -> None:
self.id : int = id
self._loaded : bool = False
self._data : typing.Union[str,None] = None
def data(self: "Example") -> str:
if not self._loaded:
self.load()
return self._data
def load(self: "Example") -> None:
self._loaded = True
# some expensive computations
self._data = f"real_data{self.id}"
def mocked_load(self: "Example") -> None:
# mock the side effects of load without the expensive computation.
self._loaded = True
self._data = f"test_data{self.id}"
class TestExample( unittest.TestCase ):
@unittest.mock.patch.object(Example, "load", new = mocked_load)
def test_data__patch_new(
self: "TestExample",
) -> None:
# This works but just replaces the Example.load function with another
# rather than wrapping it in a Mock; so you cannot assert how many
# times the patched method was called.
example1 = Example(id=1)
example2 = Example(id=2)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
@unittest.mock.patch.object(Example, "load")
def test_data__patch_side_effect(
self: "TestExample",
patched_load: unittest.mock.Mock
) -> None:
# This fails as the self argument is not passed to the side_effect
# function.
patched_load.side_effect = mocked_load
example1 = Example(id=1)
example2 = Example(id=2)
self.assertEqual(patched_load.call_count, 0)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
self.assertEqual(patched_load.call_count, 1)
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
self.assertEqual(patched_load.call_count, 2)
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
self.assertEqual(patched_load.call_count, 2)
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
self.assertEqual(patched_load.call_count, 2)
@unittest.mock.patch.object(Example, "load")
def test_data__patch_multiple_side_effect(
self: "TestExample",
patched_load: unittest.mock.Mock
) -> None:
# This passes but feels (very) wrong as you have to have change the
# side_effect each time you call the function and relies on hardcoding
# the class instances being passed as "self".
example1 = Example(id=1)
example2 = Example(id=2)
side_effect1 = lambda: mocked_load( example1 )
side_effect2 = lambda: mocked_load( example2 )
patched_load.side_effect = side_effect1
self.assertEqual(patched_load.call_count, 0)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
self.assertEqual(patched_load.call_count, 1)
patched_load.side_effect = side_effect2
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
self.assertEqual(patched_load.call_count, 2)
patched_load.side_effect = side_effect1
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
self.assertEqual(patched_load.call_count, 2)
patched_load.side_effect = side_effect2
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
self.assertEqual(patched_load.call_count, 2)
if __name__ == '__main__':
unittest.main()
如何“修复”我的第二次尝试(或提供替代方法)Example.load
用 a 修补函数,Mock
以便side_effect
可以调用对 有副作用的函数self
?
解决方案
直接从这个问题tbh:使用 autospec=True 模拟我在 python3 上工作时:
# test.py
import unittest
from unittest.mock import patch
class TestStringMethods(unittest.TestCase):
@patch.object(Example, "load", autospec=True)
def test_data__patch_side_effect(
self: "TestExample",
patched_load: unittest.mock.Mock
) -> None:
patched_load.side_effect = mocked_load
example1 = Example(id=1)
example2 = Example(id=2)
self.assertEqual(patched_load.call_count, 0)
data1_1 = example1.data()
self.assertEqual(data1_1, "test_data1")
self.assertEqual(patched_load.call_count, 1)
data2_1 = example2.data()
self.assertEqual(data2_1, "test_data2")
self.assertEqual(patched_load.call_count, 2)
data1_2 = example1.data()
self.assertEqual(data1_2, "test_data1")
self.assertEqual(patched_load.call_count, 2)
data2_2 = example2.data()
self.assertEqual(data2_2, "test_data2")
self.assertEqual(patched_load.call_count, 2)
输出:
$ python3 -m unittest test
.
----------------------------------------------------------------------
Ran 1 test in 0.001s
OK
从文档:
更强大的规范形式是 autospec。如果您设置 autospec=True ,则将使用被替换对象的规范创建模拟。
基于那里的同一段落,您可以使用对象来定义您想要的规范(作为替代方案)。以下内容也对我有用:
@patch.object(Example, "load", autospec=Example.load)