1. 概述

Mock测试是在测试过程中对可能不稳定、有副作用、不容易构造或者不容易获取的对象，用一个虚拟的对象来创建以便完成测试的方法。在Python中这种测试是通过第三方的mock库完成的，mock在Python3.3的时候被引入到Python标准库中，改名为unittest.mock。之前的Python版本都需要安装：pip install mock

初学者理解mock比较抽象，可以简单理解为函数指针，通过mock成员方法或变量，可以指定mock对象的返回值，获取是否被调用、被调用次数、调用时的参数等。

2. 使用方法

2.1. 简介

• 在test方法前，添加decorator @mock.patch('pyfile.func', return_value='None')，可以完成对pyfile.func的mock，并指定return_value为‘None’，在test方法的参数中增加mock_func即可
• 单个test方法引用多个mock.patch decorator时，patch从下向上，test方法的参数从左向右，依次对应（可以有剩余的参数,但是必学是已经声明的fixture），样例如下

@mock.patch('os.remove')
@mock.patch('os.listdir')
@mock.patch('shutil.copy')
def test_unix_fs(mocked_copy, mocked_listdir, mocked_remove):
    UnixFS.rm('file')
    os.remove.assert_called_once_with('file')

    assert UnixFS.ls('dir') == expected
    # ...

    UnixFS.cp('src', 'dst')
    # ...

2.2. 示例代码

pytest2.py

# -*- coding:utf-8 -*-
import pytest
import mock

@pytest.fixture(scope='function', params=[1, 2, 3])    # multiple test cases
def mock_data_params(request):
    return request.param

def test_not_2(mock_data_params):
    print('test_data: %s' % mock_data_params)
    assert mock_data_params != 2

##################

def _call(x):
    return '{} _call'.format(x)

def func(x):
    return '{} func'.format(_call(x))

def test_func_normal():
    for x in [11, 22, 33]:                          # multiple test cases
        # print '{} - {}'.format(x, func(x))
        assert func(x) == '{} _call func'.format(x)

@mock.patch('pytest2._call', return_value='None')   # set mock 'pytest2._call'.return_value is 'None', also could use mock_call.return_value='None'
def test_func_mock(mock_call):
    for x in [11, 22, 33]:
        # print '{} - {}'.format(x, func(x))
        ret = func(x)
        assert mock_call.called                 # True or False
        assert mock_call.call_args == ((x,),)   # This is either None (if the mock hasn’t been called), or the arguments that the mock was last called with
        assert ret == 'None func'               # because mock_call.return_value is 'None', so the result here is 'None func'

如何获取mock方法的调用次数和参数数据

• mock_call.called # True or False

• mock_call.call_args # This is either None (if the mock hasn’t been called), or the arguments that the mock was last called with

• mock_call.return_value

  
  image.png

• mock_call.side_effect # This can either be a function to be called when the mock is called, an iterable or an exception (class or instance) to be raised

  
  image.png

详细内容参考官网

• Python3 unittest.mock.Mock
  https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock
• pytest-mock
  https://pypi.python.org/pypi/pytest-mock
• pytest-mock github
  https://github.com/pytest-dev/pytest-mock/

2.3. 执行结果

通过fixture的param功能，完成多用例测试

$ pytest -v pytest2.py::test_not_2
============================================================================== test session starts ===============================================================================
platform linux2 -- Python 2.7.14, pytest-3.0.0, py-1.5.2, pluggy-0.3.1 -- /home/kevin/soft/anaconda2/bin/python
cachedir: .cache
Using --randomly-seed=1522926920
rootdir: /home/kevin/learn/python-web/tox/case2, inifile:
plugins: randomly-1.0.0, mock-1.2, cov-2.0.0
collected 3 items

pytest2.py::test_not_2[3] PASSED
pytest2.py::test_not_2[2] FAILED
pytest2.py::test_not_2[1] PASSED

==================================================================================== FAILURES ====================================================================================
_________________________________________________________________________________ test_not_2[2] __________________________________________________________________________________

mock_data_params = 2

    def test_not_2(mock_data_params):
        print('test_data: %s' % mock_data_params)
>       assert mock_data_params != 2
E       assert 2 != 2

pytest2.py:10: AssertionError
------------------------------------------------------------------------------ Captured stdout call ------------------------------------------------------------------------------
test_data: 2
============================================================================= pytest-warning summary =============================================================================
WC1 None pytest_funcarg__cov: declaring fixtures using "pytest_funcarg__" prefix is deprecated and scheduled to be removed in pytest 4.0.  Please remove the prefix and use the @pytest.fixture decorator instead.
============================================================= 1 failed, 2 passed, 1 pytest-warnings in 0.02 seconds ==============================================================

在test方法中通过循环dataset完成多用例测试

$ pytest -vs pytest2.py::test_func_normal
============================================================================== test session starts ===============================================================================
platform linux2 -- Python 2.7.12, pytest-3.0.0, py-1.5.2, pluggy-0.3.1 -- /usr/bin/python
cachedir: .cache
Using --randomly-seed=1522930543
rootdir: /home/kevin/learn/python-web/tox/case2, inifile:
plugins: xdist-1.15.0, randomly-1.0.0, mock-1.2, cov-2.0.0, celery-4.0.1
collected 6 items

pytest2.py::test_func_normal PASSED

============================================================================= pytest-warning summary =============================================================================
WC1 None pytest_funcarg__cov: declaring fixtures using "pytest_funcarg__" prefix is deprecated and scheduled to be removed in pytest 4.0.  Please remove the prefix and use the @pytest.fixture decorator instead.
================================================================== 1 passed, 1 pytest-warnings in 0.01 seconds ===================================================================

通过mock，构造虚拟函数的调用

$ pytest -vs pytest2.py::test_func_mock
============================================================================== test session starts ===============================================================================
platform linux2 -- Python 2.7.12, pytest-3.0.0, py-1.5.2, pluggy-0.3.1 -- /usr/bin/python
cachedir: .cache
Using --randomly-seed=1522930553
rootdir: /home/kevin/learn/python-web/tox/case2, inifile:
plugins: xdist-1.15.0, randomly-1.0.0, mock-1.2, cov-2.0.0, celery-4.0.1
collected 6 items

pytest2.py::test_func_mock PASSED

============================================================================= pytest-warning summary =============================================================================
WC1 None pytest_funcarg__cov: declaring fixtures using "pytest_funcarg__" prefix is deprecated and scheduled to be removed in pytest 4.0.  Please remove the prefix and use the @pytest.fixture decorator instead.
================================================================== 1 passed, 1 pytest-warnings in 0.00 seconds ===================================================================

3. 参考

• pytest
  https://docs.pytest.org/en/latest/example/markers.html
• pytest-mock
  https://pypi.python.org/pypi/pytest-mock
• Python3 unittest.mock.Mock
  https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock