unittest.mock is a library for testing in Python. It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used.
>>> from unittest.mock import MagicMock
>>> mock = MagicMock(return_value=3)
>>> # mock = MagicMock()
>>> # mock.return_value = 3
>>> mock()
定义变化的返回值
>>> mock = MagicMock(side_effect=[1, 2, 3])
# >>> mock = MagicMock()
# >>> mock.side_effect = [1, 2, 3]
>>> mock()
>>> mock()
>>> mock()
>>> mock()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 939, in __call__
return _mock_self._mock_call(*args, **kwargs)
File "/xxx/lib/python3.6/unittest/mock.py", line 998, in _mock_call
result = next(effect)
StopIteration
>>> def side_effect(arg=1):
... return arg
>>> m = MagicMock(side_effect=side_effect)
>>> m(1)
>>> m(2)
定义抛出异常
>>> m.side_effect = KeyError
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/python3.6/unittest/mock.py", line 939, in __call__
return _mock_self._mock_call(*args, **kwargs)
File "/xxx/python3.6/unittest/mock.py", line 995, in _mock_call
raise effect
KeyError
>>> from unittest.mock import patch
>>> m = MagicMock()
>>> m.test = MagicMock(return_value=233)
<MagicMock name='mock()' id='4372854824'>
>>> m.test
<MagicMock name='mock.test' id='4372854768'>
>>> m.test()
>>> import example
>>> example.foo
>>> example.hello()
'test'
>>> with patch.object(example, 'foo', {'lalala': 233}):
... example.foo
{'lalala': 233}
>>> example.foo
>>> with patch.object(example.fb, 'msg', 666):
... example.hello()
>>> example.hello()
'test'
mock dict
>>> foo = {'a': 233}
>>> foo['a']
>>> with patch.dict(foo, {'a': 666, 'b': 222}):
... print(foo['a'])
... print(foo['b'])
>>> foo['a']
>>> 'b' in foo
False
>>> with patch.dict(foo, a=666, b=222):
... print(foo['a'])
... print(foo['b'])
>>> foo['a']
>>> with patch('example.bar', MagicMock(return_value=233)):
... example.bar()
>>> with patch.object(example, 'bar', MagicMock(return_value=233)):
... example.bar()
... example.bar(233)
>>> with patch.object(example, 'bar', autospec=True) as bar:
... bar.return_value = 666
... example.bar()
>>> with patch.object(example, 'bar', autospec=True):
... example.bar(233)
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
File "<string>", line 2, in bar
File "/xxx/lib/python3.6/unittest/mock.py", line 171, in checksig
sig.bind(*args, **kwargs)
File "/xxx/lib/python3.6/inspect.py", line 2934, in bind
return args[0]._bind(args[1:], kwargs)
File "/xxx/lib/python3.6/inspect.py", line 2855, in _bind
raise TypeError('too many positional arguments') from None
TypeError: too many positional arguments
autospec=True 可以保证 mock 后的对象拥有跟原来一样的函数签名。
mock 方法
>>> example.foobar()
'hello'
>>> with patch('example.FooBar') as mocked_cls:
... instance = MagicMock()
... instance.hello = MagicMock(return_value='mocked_hello_method')
... mocked_cls.return_value = instance
... example
.foobar()
'mocked_hello_method'
>>> f.bar
>>> with patch('__main__.Foo.bar', new_callable=PropertyMock) as mock_bar:
... mock_bar.return_value = 'mocked_bar'
... foo = Foo()
... print(foo.bar)
... foo.bar = 266
... print(foo.bar)
mocked_bar
mocked_bar
>>> mock_bar
<PropertyMock name='bar' id='4373101536'>
>>> mock_bar.mock_calls
[call(), call(266), call()]
>>> with patch.object(__builtins__, 'str', int):
... test.to_str('233')
... test.to_str('foobar')
Traceback (most recent call last):
File "<stdin>", line 3, in <module>
File "/xxx/test.py", line 2, in to_str
return str(obj)
ValueError: invalid literal for int() with base 10: 'foobar'
>>> from unittest.mock import mock_open
>>> m = mock_open(read_data='mocked data')
>>> with patch('__main__.open', m):
... with open('test') as fp:
... print(fp.read())
mocked data
<MagicMock name='open' spec='builtin_function_or_method' id='4369854192'>
>>> m.mock_calls
[call('test'),
call().__enter__(),
call().read(),
call().__exit__(None, None, None)]
write:
>>> m2 = mock_open()
>>> with patch('__main__.open', m2):
... with open('bar', 'w') as fp:
... fp.write('write data')
>>> m2.mock_calls
[call('bar', 'w'),
call().__enter__(),
call().write('write data'),
call().__exit__(None, None, None)]
>>> m2().write.mock_calls
[call('write data')]
mock 真值判断
可以通过 mock __bool__ 方法（Python 3） 或 __nonzero__ 方法(Python 2) 来 mock 对对象的真值判断:
>>> m = MagicMock()
>>> bool(m)
>>> m = MagicMock(__bool__=MagicMock(return_value=False))
>>> bool(m)
False
>>> if not m: print('false')
false
mock 特殊属性
所谓的特殊属性就是 Mock/MagicMock 对象自带的属性（自带一些可选参数 ），
比如 name ， 如果我们要 mock 的对象也有一个 name 属性的话，
通过 MagicMock(name='foo') 是无法 mock name 这个属性的，
可以用下面两种方法实现 mock 特殊属性:
覆盖 mock 对象的属性:
>>> m = MagicMock(name='foo')
>>> m.name
<MagicMock name='foo.name' id='4372898816'>
>>> m = MagicMock()
>>> m.name = 'foo'
>>> m.name
'foo'
使用 configure_mock:
>>> m = MagicMock()
>>> m.name
<MagicMock name='mock.name' id='4373042848'>
>>> m.configure_mock(name='foo')
>>> m.name
'foo'
自动撤销 mock
patch, patch.object 都支持通过 with 语句或者装饰器可以实现
只在指定函数/方法/块中应用 mock ，函数/方法/块结束后自动撤销 mock
>>> str('abc')
'abc'
>>> with patch.object(__builtins__, 'str', int):
... str('abc')
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
ValueError: invalid literal for int() with base 10: 'abc'
>>> str('abc')
'abc'
>>> @patch.object(__builtins__, 'str', int)
... def test():
... str('abc')
>>> str('abc')
'abc'
>>> test()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 1179, in patched
return func(*args, **keywargs)
File "<stdin>", line 3, in test
ValueError: invalid literal for int() with base 10: 'abc'
<MagicMock name='mock()' id='4372904760'>
>>> m(2)
<MagicMock name='mock()' id='4372904760'>
>>> m(3)
<MagicMock name='mock()' id='4372904760'>
.called: 是否被调用过
>>> m.called
.call_count: 获取调用次数
>>> m.call_count
.assert_called(): 检查是否被调用过，如果没有被调用过，则会抛出 AssertionError 异常
>>> m.assert_called()
.assert_called_once(): 确保调用过一次，如果没调用或多于一次，则抛出 AssertionError 异常
>>> m.assert_called_once()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 795, in assert_called_once
raise AssertionError(msg)
AssertionError: Expected 'mock' to have been called once. Called 3 times.
.assert_not_called(): 确保没被调用过，否则抛出 AssertionError 异常
>>> m.assert_not_called()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 777, in assert_not_called
raise AssertionError(msg)
AssertionError: Expected 'mock' to not have been called. Called 3 times.
检查调用时使用的参数
待检查的 mock 对象:
>>> m = MagicMock()
>>> m(1, 2, foo='bar')
<MagicMock name='mock()' id='4372980792'>
.call_args: 最后一次调用时使用的参数，未调用则返回 None
>>> m.call_args
call(1, 2, foo='bar')
.assert_called_once_with(*args, **kwargs): 确保只调用过一次，并且使用特定参数调用
>>> m.assert_called_once_with(1, 2, foo='bar')
>>> m(2)
<MagicMock name='mock()' id='4372980792'>
>>> m.assert_called_once_with(1, 2, foo='bar')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 824, in assert_called_once_with
raise AssertionError(msg)
AssertionError: Expected 'mock' to be called once. Called 2 times.
.assert_any_call(*args, **kwargs): 检查某次用特定参数进行过调用
>>> m.assert_any_call(1, 2, foo='bar')
.assert_called_with(*args, **kwargs): 检查最后一次调用时使用的参数
>>> m.assert_called_with(2)
>>> m.assert_called_with(1, 2, foo='bar')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 814, in assert_called_with
raise AssertionError(_error_message()) from cause
AssertionError: Expected call: mock(1, 2, foo='bar')
Actual call: mock(2)
.call_args_list: 所有调用时使用的参数列表
>>> m.call_args_list
[call(1, 2, foo='bar'), call(2)]
>>> m(3)
<MagicMock name='mock()' id='4372980792'>
>>> m.call_args_list
[call(1, 2, foo='bar'), call(2), call(3)]
.assert_has_calls(calls, any_order=False): 检查某几次调用时使用的参数，
如果 any_order 为 False 时必须是挨着的调用顺序，可以是中间的几次调用，
为 True 时 calls 中的记录可以是无序的
>>> from unittest.mock import call
>>> m.call_args_list
[call(1, 2, foo='bar'), call(2), call(3)]
>>> m.assert_has_calls([call(2), call(3)])
>>> m.assert_has_calls([call(3), call(2)])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/xxx/lib/python3.6/unittest/mock.py", line 846, in assert_has_calls
) from cause
AssertionError: Calls not found.
Expected: [call(3), call(2)]
Actual: [call(1, 2, foo='bar'), call(2), call(3)]
>>> m.assert_has_calls([call(3), call(2)], any_order=True)
.method_calls: mock 对象的方法调用记录
>>> m.test_method(2, 3, 3)
<MagicMock name='mock.test_method()' id='4372935456'>
>>> m.method_calls
[call.test_method(2, 3, 3)]
.mock_calls: 记录 mock 对象的所有调用，包含方法、magic method 以及返回值 mock
>>> m.mock_calls
[call(1, 2, foo='bar'), call(2), call(3), call.test_method(2, 3, 3)]
>>> m.call_args_list
[call(1, 2, foo='bar'), call(2), call(3)]
手动重置 mock 调用记录
可以使用 .reset_mock() 重置 mock 对象记录的调用记录:
>>> m.mock_calls
[call(1, 2, foo='bar'), call(2), call(3), call.test_method(2, 3, 3)]
>>> m.call_args_list
[call(1, 2, foo='bar'), call(2), call(3)]
>>> m.reset_mock()
>>> m.call_args_list
>>> m.mock_calls
· Privacy 
"mozillazg's Blog" by mozillazg is
licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where indicated otherwise.
