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Django项目test中的mock概述
本文环境python3.5.2
test中的mock实现
接口示例代码如下；
...
# 路由配置
('^api/business_application/?$', TestAPI.as_view()),
...
# 接口函数 app_name.apis.py
from rest_framework.generics import GenericAPIView
from rest_framework.response import Response
def mock_test(test_val):
print("test_mock_val")
return "real_return" + test_val
class TestAPI(GenericAPIView):
view_name = 'test'
def get(self, request):
data = mock_test("real")
return Response({"detail": data})
test测试代码如下：
from unittest.mock import patch
from django.test import TestCase
class MockAPITest(TestCase):
"""mock测试"""
def setUp(self):
self.url = reverse('app_name:test')
@patch('app_name.apis.mock_test')
def test_post(self, mock_test):
mock_test.return_value = "mock"
resp = self.client.get(self.url)
retdata = resp.data
self.assertEqual(retdata['detail'], "mock")
此时在终端中，运行该用例测试结果正常，此时分析一下在该示例中mock的基本用法，由于本次测试的场景相对简单故在源码分析中，复杂的场景就不详细分析。
unittest.mock中的patch分析
首先查看patch函数的执行流程如下；
def _dot_lookup(thing, comp, import_path):
try:
return getattr(thing, comp) # 获取导入的属性
except AttributeError:
__import__(import_path)
return getattr(thing, comp)
def _importer(target):
components = target.split('.') # 此时传入的target为app_name.apis
import_path = components.pop(0) # 获取app_name
thing = __import__(import_path) # 导入app_name
for comp in components:
import_path += ".%s" % comp # 遍历路径名称
thing = _dot_lookup(thing, comp, import_path) # 依次获取导入的属性名称
return thing # 遍历完成后此时就获取到了 mock_test对应的方法属性
def _get_target(target):
try:
target, attribute = target.rsplit('.', 1) # 获取module路径 和方法名称，app_name.apis 和 mock_test方法
except (TypeError, ValueError):
raise TypeError("Need a valid target to patch. You supplied: %r" %
(target,))
getter = lambda: _importer(target) # 封装成函数等待调用
return getter, attribute # 返回
def patch(
target, new=DEFAULT, spec=None, create=False,
spec_set=None, autospec=None, new_callable=None, **kwargs
):
getter, attribute = _get_target(target) # 获取传入的属性对应的值
return _patch(
getter, attribute, new, spec, create,
spec_set, autospec, new_callable, kwargs
)
此时先去导入相关的module，去获取对应mock函数的函数，然后再传入_patch类中进行初始化，
class _patch(object):
attribute_name = None
_active_patches = []
def __init__(
self, getter, attribute, new, spec, create,
spec_set, autospec, new_callable, kwargs
):
if new_callable is not None:
if new is not DEFAULT:
raise ValueError(
"Cannot use 'new' and 'new_callable' together"
)
if autospec is not None:
raise ValueError(
"Cannot use 'autospec' and 'new_callable' together"
)
self.getter = getter # 属性获取对应
self.attribute = attribute # 属性方法
self.new = new
self.new_callable = new_callable
self.spec = spec
self.create = create
self.has_local = False
self.spec_set = spec_set
self.autospec = autospec
self.kwargs = kwargs
self.additional_patchers = []
def copy(self):
patcher = _patch(
self.getter, self.attribute, self.new, self.spec,
self.create, self.spec_set,
self.autospec, self.new_callable, self.kwargs
)
patcher.attribute_name = self.attribute_name
patcher.additional_patchers = [
p.copy() for p in self.additional_patchers
]
return patcher
def __call__(self, func):
if isinstance(func, type): # 在测试中调用的该方法
return self.decorate_class(func)
return self.decorate_callable(func)
由于先前博文已经分析过test的执行过程，此时test会执行到test(result)函数方法，由于本例中的test_post由装饰器patch修饰，此时返回的是_patch类的实例，当调用test_post方法时，就会调用__call__方法，由于此时test_post是一个call_func所以会执行到self.decorate_callable函数处，该函数如下；
def decorate_callable(self, func):
if hasattr(func, 'patchings'): # 检查func是否有patching属性，该属性为一个列表，该属性用于存放_patch对象，处理一个方法经过了多个_patch对象装饰
func.patchings.append(self) # 如果有则添加到该属性列表中
return func # 返回该函数
@wraps(func)
def patched(*args, **keywargs): # 当test真正执行时，调用该方法
extra_args = [] # 传入参数
entered_patchers = []
exc_info = tuple() # 报错信息
try:
for patching in patched.patchings: # 遍历patchings列表
arg = patching.__enter__() # 调用_patch的__enter__方法
entered_patchers.append(patching) # 添加到entered_patchers列表中
if patching.attribute_name is not None: # 检查_patch对应的需要mock的方法名是否为空
keywargs.update(arg) # 不为空则更新传入参数
elif patching.new is DEFAULT:
extra_args.append(arg) # 检查传入的是否是默认参数，如果没有使用位置参数则使用位置参数
args += tuple(extra_args) # 增加到位置参数中
return func(*args, **keywargs) # 调用该test对应的方法，本例中为test_post方法
except:
if (patching not in entered_patchers and
_is_started(patching)): # 报错处理
# the patcher may have been started, but an exception
# raised whilst entering one of its additional_patchers
entered_patchers.append(patching)
# Pass the exception to __exit__
exc_info = sys.exc_info()
# re-raise the exception
raise
finally:
for patching in reversed(entered_patchers): # 执行正确最后执行_patch对应的__exit__方法
patching.__exit__(*exc_info)
patched.patchings = [self] # 添加该属性
return patched # 返回该patched方法
该函数主要就是执行了包装后的_patch方法，依次执行_patch的__enter__方法，当执行完成后，依次调用_patch的__exit__的方法，此时就依次完成对测试用例的执行，继续查看_patch对应的__enter__方法；
def get_original(self):
target = self.getter() # 获取命名空间的module
name = self.attribute # 获取需要Mock的函数名
original = DEFAULT # 默认为DEFAULT
local = False # 是否本地空间中找到 默认为False
try:
original = target.__dict__[name] # 获取需要mock的函数，在本例中因为在同一命名空间中，是可以获取到该函数
except (AttributeError, KeyError):
original = getattr(target, name, DEFAULT)
else:
local = True # 修改标志位
if name in _builtins and isinstance(target, ModuleType): # 判断是否为在内建名称中，判断target是否为module
self.create = True
if not self.create and original is DEFAULT:
raise AttributeError(
"%s does not have the attribute %r" % (target, name)
)
return original, local # 返回原始函数，是否在本地命名空间找到标志
def __enter__(self):
"""Perform the patch."""
new, spec, spec_set = self.new, self.spec, self.spec_set
autospec, kwargs = self.autospec, self.kwargs
new_callable = self.new_callable # 获取初始化时传入的new_callable方法
self.target = self.getter() # 获取对应的moduel
# normalise False to None # 一般情况下设置为空或者False
if spec is False:
spec = None
if spec_set is False:
spec_set = None
if autospec is False:
autospec = None
if spec is not None and autospec is not None:
raise TypeError("Can't specify spec and autospec")
if ((spec is not None or autospec is not None) and
spec_set not in (True, None)):
raise TypeError("Can't provide explicit spec_set *and* spec or autospec")
original, local = self.get_original() # 获取被mock函数的原始函数，是否在module的命名空间中找到
if new is DEFAULT and autospec is None: # 本例中new为DEFAULT autospec为None
inherit = False # 是否继承
if spec is True:
# set spec to the object we are replacing
spec = original
if spec_set is True:
spec_set = original
spec = None
elif spec is not None:
if spec_set is True:
spec_set = spec
spec = None
elif spec_set is True:
spec_set = original
if spec is not None or spec_set is not None:
if original is DEFAULT:
raise TypeError("Can't use 'spec' with create=True")
if isinstance(original, type):
# If we're patching out a class and there is a spec
inherit = True
Klass = MagicMock # 设置MagicMock类，该类就是替代mock的函数的类
_kwargs = {} # 设置类的传入的位置参数
if new_callable is not None: # 如果在传入的时候指定了new_callable函数
Klass = new_callable # 使用传入的类作为mock的类实例
elif spec is not None or spec_set is not None:
this_spec = spec
if spec_set is not None:
this_spec = spec_set
if _is_list(this_spec):
not_callable = '__call__' not in this_spec
else:
not_callable = not callable(this_spec)
if not_callable:
Klass = NonCallableMagicMock
if spec is not None:
_kwargs['spec'] = spec
if spec_set is not None:
_kwargs['spec_set'] = spec_set
# add a name to mocks
if (isinstance(Klass, type) and
issubclass(Klass, NonCallableMock) and self.attribute): # 判断是否是类，是否是NonCallableMock子类，并且传入了mock的函数名称
_kwargs['name'] = self.attribute # 设置名称为mock的函数名
_kwargs.update(kwargs) # 更新传入参数
new = Klass(**_kwargs) # 实例化一个实例
if inherit and _is_instance_mock(new):
# we can only tell if the instance should be callable if the
# spec is not a list
this_spec = spec
if spec_set is not None:
this_spec = spec_set
if (not _is_list(this_spec) and not
_instance_callable(this_spec)):
Klass = NonCallableMagicMock
_kwargs.pop('name')
new.return_value = Klass(_new_parent=new, _new_name='()',
**_kwargs)
elif autospec is not None:
# spec is ignored, new *must* be default, spec_set is treated
# as a boolean. Should we check spec is not None and that spec_set
# is a bool?
if new is not DEFAULT:
raise TypeError(
"autospec creates the mock for you. Can't specify "
"autospec and new."
)
if original is DEFAULT:
raise TypeError("Can't use 'autospec' with create=True")
spec_set = bool(spec_set)
if autospec is True:
autospec = original
new = create_autospec(autospec, spec_set=spec_set,
_name=self.attribute, **kwargs)
elif kwargs:
# can't set keyword args when we aren't creating the mock
# XXXX If new is a Mock we could call new.configure_mock(**kwargs)
raise TypeError("Can't pass kwargs to a mock we aren't creating")
new_attr = new # 赋值
self.temp_original = original # 保存旧函数到temp_original属性上
self.is_local = local # 保存是否在本地找到标志位
setattr(self.target, self.attribute, new_attr) # 设置属性值到module中，替换原来的属性值，此时本例中的mock_test就被替换为MagicMock类的实例
if self.attribute_name is not None: # 如果传入的属性值不为空
extra_args = {}
if self.new is DEFAULT: # 判断是否为DEFAULT
extra_args[self.attribute_name] = new # 设置到传入参数中
for patching in self.additional_patchers:
arg = patching.__enter__()
if patching.new is DEFAULT:
extra_args.update(arg)
return extra_args
return new
此时就将app_name.apis中的命名为mock_test的函数的名称替换为了对应的MagicMock类实例，此时在调用mock_test函数时，就是调用的MagicMock的__call__方法，在详细查看MagicMock的继承关系后，可以知道最终会调用到CallableMixin类的__call__方法，
def _mock_check_sig(self, *args, **kwargs):
# stub method that can be replaced with one with a specific signature
pass
def __call__(_mock_self, *args, **kwargs):
# can't use self in-case a function / method we are mocking uses self
# in the signature
_mock_self._mock_check_sig(*args, **kwargs) # 检查
return _mock_self._mock_call(*args, **kwargs) # 执行
此时继续查看_mock_call方法，由于本例中只涉及到了简单的情况，故复杂的业务场景没有详细分析；
def _mock_call(_mock_self, *args, **kwargs):
self = _mock_self
self.called = True
self.call_count += 1 # 调用次数加1
_new_name = self._mock_new_name # 获取mock的名称
_new_parent = self._mock_new_parent
_call = _Call((args, kwargs), two=True) # 包装传入参数
self.call_args = _call
self.call_args_list.append(_call)
self.mock_calls.append(_Call(('', args, kwargs)))
seen = set()
skip_next_dot = _new_name == '()'
do_method_calls = self._mock_parent is not None
name = self._mock_name
while _new_parent is not None: # 如果_new_parent不为空
this_mock_call = _Call((_new_name, args, kwargs))
if _new_parent._mock_new_name:
dot = '.'
if skip_next_dot:
dot = ''
skip_next_dot = False
if _new_parent._mock_new_name == '()':
skip_next_dot = True
_new_name = _new_parent._mock_new_name + dot + _new_name
if do_method_calls:
if _new_name == name:
this_method_call = this_mock_call
else:
this_method_call = _Call((name, args, kwargs))
_new_parent.method_calls.append(this_method_call)
do_method_calls = _new_parent._mock_parent is not None
if do_method_calls:
name = _new_parent._mock_name + '.' + name
_new_parent.mock_calls.append(this_mock_call)
_new_parent = _new_parent._mock_new_parent
# use ids here so as not to call __hash__ on the mocks
_new_parent_id = id(_new_parent)
if _new_parent_id in seen:
break
seen.add(_new_parent_id)
ret_val = DEFAULT # 返回值默认设置为DEFAULT
effect = self.side_effect # 获取effect值
if effect is not None:
if _is_exception(effect):
raise effect
if not _callable(effect):
result = next(effect)
if _is_exception(result):
raise result
if result is DEFAULT:
result = self.return_value
return result
ret_val = effect(*args, **kwargs)
if (self._mock_wraps is not None and
self._mock_return_value is DEFAULT):
return self._mock_wraps(*args, **kwargs)
if ret_val is DEFAULT: # 判断ret_val是否为默认值
ret_val = self.return_value # 如果是默认值则直接设置 为类的return_value值，在本例中在被设置为字符串"mock"
return ret_val # 返回 "mock"
此时该mock的函数就返回了在测试中设置的字符串"mock"，此时在测试api执行的过程中就返回了该值。在__enter__执行完成，就完成了对Mock函数的最终的执行，在执行完成之后，还需要调用__exit__进行最终的相关属性的恢复；
def __exit__(self, *exc_info):
"""Undo the patch."""
if not _is_started(self):
raise RuntimeError('stop called on unstarted patcher')
if self.is_local and self.temp_original is not DEFAULT: # 还原相关属性，将被Mock的属性还原为真是的函数
setattr(self.target, self.attribute, self.temp_original)
else:
delattr(self.target, self.attribute) # 先删除
if not self.create and (not hasattr(self.target, self.attribute) or
self.attribute in ('__doc__', '__module__',
'__defaults__', '__annotations__',
'__kwdefaults__')):
# needed for proxy objects like django settings
setattr(self.target, self.attribute, self.temp_original) # 再还原
del self.temp_original # 删除相关属性值
del self.is_local
del self.target
for patcher in reversed(self.additional_patchers):
if _is_started(patcher):
patcher.__exit__(*exc_info)
至此，一个简单的测试的mock的过程就分析完成。本文基于了一个最简单的场景大致分析了该流程。
总结
本文简单的分析了mock该方法，在Django项目中的最简单的使用场景，mock的实现原理可以简单的描述为，通过导入相关模块，然后通过更新该模块对应的该函数的实例，通过该实例在被其他函数调用时，直接更改为我们期望的返回值，以此达到模拟假数据的返回，如有疏漏请批评指正。