这里的构造器是指的mock对象的__init__方法，我们在这里称为构造器。通常在使用过程中需要自定义一些属性，使之适应具体情形。
先产生一个mock对象
from unittest import mock
m = mock.Mock()
print(m)
result:
<Mock id='2100066382344'>
1 name属性
mock对象的名字，起到一个标识的作用。
先来看一下原始的mock对象的名字
print(m.name)
result:
<Mock name='mock.name' id='2239287237256'>
再来看一下mock对象自定义name属性之后的名字
m.name = 'test_mock'
print(m.name)
result:
test_mock
2 return_value属性
该参数用于返回自己模拟的返回值，当要测试的接口类或者方法未开发完成时，使用这个值来代替真实的返回值。
from unittest import mock
import unittest
# 测试用例类
class SumTest(unittest.TestCase):
def test(self):
sum_result = mock.Mock(return_value=40)
print(sum_result())
if __name__ == '__main__':
sum_test = SumTest()
sum_test.test()
result:
Testing started at 19:57 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
Ran 1 test in 0.003s
OK
40
Process finished with exit code 0
3 side_effect属性
3.1 side_effect作用
如果side_effect和return_value同时存在的时候，side_effect将会覆盖return_value。所以如果要使用return_value,切记不能设置side_effect属性。
from unittest import mock
import unittest
# 测试用例类
class SumTest(unittest.TestCase):
def test(self):
sum_result = mock.Mock(return_value=40, side_effect=[12])
print(sum_result())
result:
Testing started at 19:57 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
Ran 1 test in 0.003s
OK
12
Process finished with exit code 0
这里return_value的值为15，side_effect的值为12，由于side_effect覆盖了return_value，所以最后的结果为side_effect的值， 12
3.2 side_effect对象本质
side_effect对象本质上是一个迭代器,对其就可以进行多次调用。
from unittest import mock
import unittest
# 测试用例类
class SumTest(unittest.TestCase):
def test(self):
sum_result = mock.Mock(return_value=40, side_effect=[12, 15])
print(sum_result())
print(sum_result())
print(sum_result())
result:
Testing started at 20:00 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
12
15
Ran 1 test in 0.005s
FAILED (errors=1)
Error
Traceback (most recent call last):
File "D:\software\python\lib\unittest\case.py", line 59, in testPartExecutor
yield
File "D:\software\python\lib\unittest\case.py", line 628, in run
testMethod()
File "D:\python_record\mock_demo.py", line 21, in test
print(sum_result())
File "D:\software\python\lib\unittest\mock.py", line 1016, in __call__
return _mock_self._mock_call(*args, **kwargs)
File "D:\software\python\lib\unittest\mock.py", line 1078, in _mock_call
result = next(effect)
StopIteration
Process finished with exit code 1
Assertion failed
Assertion failed
Assertion failed
这里报错是因为我们为side_effect设置了长度为2，却反复调用了3次，所以触发了StopIteration异常
3.3 side_effect的使用
我们一般使用该参数来返回真实函数的返回值，当要测试的接口类或者方法已经开发完成时，使用这个值替换之前return_value所模拟的那个值。这样就可以覆盖掉mock对象部分的代码了。
3.3.1未使用side_effect之前
modular.py
class Count(object):
def add(self, a, b):
return a + b
mock_demo.py
from unittest import mock
import unittest
from modular import Count
# 测试用例类
class SumTest(unittest.TestCase):
def test(self):
count_obj = Count()
arg1 = 8
arg2 = 5
count_obj.add = mock.Mock(return_value=15)
result = count_obj.add(arg1, arg2)
print(result)
if __name__ == '__main__':
sum_test = SumTest()
sum_test.test()
result:
Testing started at 20:20 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
Ran 1 test in 0.002s
OK
15
Process finished with exit code 0
这里返回的是模拟的数值15(当然，这里为了对比，设定了一个错误的模拟值)
3.3.2 使用side_effect之后
mock_demo.py
from unittest import mock
import unittest
from modular import Count
# 测试用例类
class SumTest(unittest.TestCase):
def test(self):
count_obj = Count()
arg1 = 8
arg2 = 5
count_obj.add = mock.Mock(return_value=15, side_effect=count_obj.add)
result = count_obj.add(arg1, arg2)
print(result)
if __name__ == '__main__':
sum_test = SumTest()
sum_test.test()
result:
Testing started at 20:21 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
13
Ran 1 test in 0.002s
OK
Process finished with exit code 0
这里便调用了真实函数返回了真实的结果13，而不是事先模拟的数值15
再验证一次
modular.py
class Count(object):
def add(self, a, b):
return a * b
这里add()方法实际上变成了乘法
mock_demo.py
from unittest import mock
import unittest
from modular import Count
# 测试用例类
```
class SumTest(unittest.TestCase):
def test(self):
count_obj = Count()
arg1 = 8
arg2 = 5
count_obj.add = mock.Mock(return_value=15, side_effect=count_obj.add)
result = count_obj.add(arg1, arg2)
print(result)
if __name__ == '__main__':
sum_test = SumTest()
sum_test.test()
result:
Testing started at 20:23 ...
D:\software\python\python.exe "D:\software\PyCharm 2019.3.4\plugins\python\helpers\pycharm_jb_unittest_runner.py" --path D:/python_record/mock_demo.py
Launching unittests with arguments python -m unittest D:/python_record/mock_demo.py in D:\python_record
40
Ran 1 test in 0.002s
OK
Process finished with exit code 0
这里返回了真实的结果40，而不是模拟的结果13
