用补丁模拟两个函数以进行单元测试 [英] Mocking two functions with patch for a unit test

问题描述

我有一个要单元测试的函数包含调用其他两个函数.我不确定如何使用补丁正确地同时模拟这两个函数.我在下面提供了一个例子来说明我的意思.当我运行nosetests时，测试通过了，但我觉得必须有一种更清洁的方法来做到这一点，我并不真正理解关于f.close()的文章......

I have a function I want to unit test contains calls two other functions. I am unsure how can I mock both functions at the same time properly using patch. I have provided an example of what I mean below. When I run nosetests, the tests pass but I feel that there must be a cleaner way to do this and I do not really Understand the piece regarding f.close()...

目录结构如下:

program/
  program/
    data.py
  tests/
    data_test.py

数据.py:

import cPickle

def write_out(file_path, data):
    f = open(file_path, 'wb')
    cPickle.dump(data, f)
    f.close()

data_test.py:

data_test.py:

from mock import MagicMock, patch

def test_write_out():
    path = '~/collection'
    mock_open = MagicMock()
    mock_pickle = MagicMock()
    f_mock = MagicMock()
    with patch('__builtin__.open', mock_open):
        f = mock_open.return_value
        f.method.return_value = path
        with patch('cPickle.dump', mock_pickle):
            write_out(path, 'data')
            mock_open.assert_called_once_with('~/collection', 'wb')
            f.close.assert_any_call()
            mock_pickle.assert_called_once_with('data', f)

结果:

$ nosetests
.
----------------------------------------------------------------------
Ran 1 test in 0.008s
OK

推荐答案

您可以通过使用补丁装饰器并像这样嵌套它们来简化测试(默认情况下它们是 MagicMock 对象):

You can simplify your test by using the patch decorator and nesting them like so (they are MagicMock objects by default):

@patch('cPickle.dump')
@patch('__builtin__.open')
def test_write_out(mock_open, mock_pickle):
    path = '~/collection'
    f = mock_open.return_value
    f.method.return_value = path

    write_out(path, 'data')

    mock_open.assert_called_once_with('~/collection', 'wb')
    mock_pickle.assert_called_once_with('data', f)
    f.close.assert_any_call()

对 MagicMock 实例的调用会返回一个新的 MagicMock 实例，因此您可以检查返回的值是否像任何其他模拟对象一样被调用.在这种情况下，f 是一个名为 'open()' 的 MagicMock(尝试打印 f).

Calls to a MagicMock instance return a new MagicMock instance, so you can check that the returned value was called just like any other mocked object. In this case f is a MagicMock named 'open()' (try printing f).

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