pytest-mock 数据模拟

文章目录

  • mock 测试
  • unittest.mock
    • Mock类
    • MagicMock类
    • patch装饰器
    • create_autospec函数
    • 断言的方法
  • pytest-mock 使用

mock 测试

在单元测试时,有些数据需要依赖其他服务或者不好获取到,此时需要使用mock来模拟对应的函数、对象等。
 
mock模拟数据的python框架
unittest.mock, 标准模块;,有基于此的mock扩展包;
faker 生成假数据
pytest-mock, 扩展模块

 
mock 作用:

  • 解决web开发中,后端接口不存在时,使用mock模拟数据返回;
  • 依赖第三方接口时, mock模拟返回;
  • demo 演示效果;
     

unittest.mock

Mock类

  • 核心类Mock,基类;
  • 可以创建属性、方法,并存储如何被调用;
  • Mock实例化的参数
    • spec, 字符串列表或者对象(dir获取对象的属性名称),表示该Mock对象可以访问的属性;访问不在列表中的属性时,报错AttributeError;
    • spec_set,属于spec的严格变体,使用方法类似;
    • side_effect, 调用Mock对象时,执行的函数,常用引发异常,或者动态改变函数的返回值; 如果是可迭代对象,则每次调用Mock对象都获取一个值;
    • return_value, 指定调用Mock对象的返回值;
    • wraps,包裹的函数,Mock对象的调用,实际是包裹函数的调用,并返回,类似side_effect;
    • name, Mock对象的名称;
  • 使用方法:

from unittest.mock import Mock
class Lauf:
    def __init__(self, name, age):
    	self.name = name
        self.age = age

# 创建对象
lauf = Lauf("jack", 25)
mock_obj = Mock(spec=lauf) # mock对象具有lauf的属性、方法,可以进行属性赋值
mock_obj.name = "lili"

# side_effect 用于引发异常
mock = Mock(side_effect=KeyError('foo'))
mock()
# 抛出异常
KeyError: 'foo'
mock.side_effect = 可重新赋值

# side_effect 用于执行函数动作
m4 = Mock(side_effect=lambda: print("执行函数"))
m4()
执行函数
m4.mock_calls # 查看调用记录


# return_value 直接指定返回值
In [58]: m5 = Mock(return_value="jack")
In [59]: m5()
Out[59]: 'jack'

# wraps 包裹
In [67]: def func():
    ...:     print("func is running...")
    ...: 

In [68]: m8 = Mock(wraps=func)
In [69]: m8()
func is running...

MagicMock类

  • MagicMock是 Mock的子类,默认实现了大部分魔法方法;
  • 简单使用
from unittest.mock import MagicMock


class Lauf:
    def __init__(self, name, age):
    	self.name = name
        self.age = age

# 模拟方法
lauf.run_method = MagicMock(return_value="running...")

lauf.run_method(3,4,5,key="value") # 参数随意
'running...'

# 断言
lauf.run_method.assert_called_once_with(3,4,5,key="value") # 带着这些参数被调用一次

 

patch装饰器

  • 模拟xxx,得到一个MagicMock对象;
  • 使用:
from unittest.mock import patch

In [83]: @patch("os.path")
    ...: def func(a): # 模拟os.path得到一个MagicMock对象,传给函数
    ...:     print(a, a is os.path)
    ...: 
    ...: 

In [84]: func()
<MagicMock name='path' id='1620313178896'> True


# 依次模拟,得到多个MagicMock对象
@patch("requests.post")
@patch("requests.get")
def func(get_mock, post_mock):
	print(get_mock is requests.get) # True
	print(post_mock is requests.post) # True


# 模拟类的对象
# 为类的对象的属性、方法(必须该类中存在) 创建一个MagicMock对象
with patch.object(Lauf, 'method', return_value=None) as mock_method:
    lauf = Lauf('a', 10)
    lauf.method(1, 2, 3)

# 断言
mock_method.assert_called_once_with(1, 2, 3)


# 上下文内有效
foo = {'key': 'value'}
original = foo.copy()
with patch.dict(foo, {'newkey': 'newvalue'}, clear=True):
    assert foo == {'newkey': 'newvalue'} # 测试时foo变为新字典

# 测试结束,foo恢复
assert foo == original


# 操作魔法方法
m = MagicMock()
m.__str__.return_value = "jack"
str(m) # 返回"jack"

m.__str__ = MagicMock(return_value="xxx")

 

create_autospec函数

  • 创建mock对象,并确保与模拟的函数、对象具有相同的接口;
  • patch(autospec=True)
In [98]: def func(a,b,c):
    ...:     print(a,b,c)
    ...: 

# 模拟函数,并确保参数相同
In [99]: mock_func = create_autospec(func, return_value="3")

In [100]: mock_func(1,2,3)
Out[100]: '3'


# 模拟对象,并确保相同的接口
In [106]: mock_obj = create_autospec(Lauf("jack", 23))

In [107]: mock_obj.name
Out[107]: <NonCallableMagicMock name='mock.name' spec='str' id='1620277710272'>
mock_obj.name = "lili" # 赋值

In [108]: mock_obj.age
Out[108]: <NonCallableMagicMock name='mock.age' spec='int' id='1620302996240'>


 

断言的方法

  • assert_called()
    Assert that the mock was called at least once.
mock = Mock()
# 调用mock
mock()
# 断言
mock.assert_called()

# 返回一个新的Mock对象
mock.method()
<Mock name='mock.method()' id='...'>
# mock.xx 随即返回一个新的 mock对象,新的mock对象断言
mock.method .assert_called()
  • assert_called_once()
    Assert that the mock was called exactly once.
mock = Mock()
mock.assert_called_once()  # 仅仅调用一次,多/没调用  均异常
  • assert_called_with(*args, **kwargs)
    This method is a convenient way of asserting that the last call has been made in a particular way:

mock = Mock()
mock.method(1, 2, 3, test='wow')
mock.method.assert_called_with(1, 2, 3, test='wow')
  • assert_called_once_with(*args, **kwargs)
    Assert that the mock was called exactly once and that call was with the specified arguments.

mock = Mock(return_value=None)
mock('foo', bar='baz')
mock.assert_called_once_with('foo', bar='baz')

mock('other', bar='values')
mock.assert_called_once_with('other', bar='values')
Traceback (most recent call last):
  ...
AssertionError: Expected 'mock' to be called once. Called 2 times.

  • assert_any_call(*args, **kwargs),
    assert the mock has been called with the specified arguments.
mock = Mock(return_value=None)
mock(1, 2, arg='thing')
mock('some', 'thing', 'else')
mock.assert_any_call(1, 2, arg='thing')

 

pytest-mock 使用

  • 安装
pip install pytest pytest-mock
  • 使用

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