无法使用 mock_open() 在模拟函数中测试全局值

Question

我正在尝试使用 mock_open() 来测试我的应用程序 Mocking file reads using patch decorator and side_effect，但我无法检查 under 函数中的全局值集] 测试。它仅在函数返回值时有效。

我的应用程序代码片段类似于

#!/usr/bin/env python
 # -*- coding: utf-8 -*-

thresh_dict = {}
allowed_san_dict = {}
max_eval_count = ""
clear_eval_count = ""

def generate_cfg_thresh_map():
    """ For generating a mapping table containing the thresholds for each of the
    production devices. The file is read one line at a time and split on whitespace
    to get the individual fields
    """

    global allowed_san_dict
    global max_eval_count
    global clear_eval_count
    try:
        with open ('/opt/config/pwr_thresh_cfg', 'r') as fh:
            for line in fh:
                split_line = line.split()
                if line.startswith("ENTRY_THRESH_COUNT"):
                    max_eval_count = int(split_line[1])
                elif line.startswith("EXIT_THRESH_COUNT"):
                    clear_eval_count = int(split_line[1])
                else:
                    thresh_dict[split_line[0]]  = [int(split_line[1]), int(split_line[2]), int(split_line[3])]
                    allowed_san_dict[split_line[0]] = int(split_line[4])

    except Exception as error:
        log_to_journal('read failed from pwr_thresh_cfg')

并且 test_app.py 文件看起来像

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# Include require py.test libraries for the suite to run
import unittest
import pytest
import mock

import app

from mock import patch, mock_open

class ReportMonitor(unittest.TestCase):
    def test_generate_cfg_thresh_map(self):
        with patch('app.open', mock_open(read_data='ENTRY_THRESH_COUNT 200')) as _:
            app.generate_cfg_thresh_map()
            assert app.max_eval_count == 200
            print('value for %s' % (app.max_eval_count))
            print('value for %s' % (app.generate_cfg_thresh_map()))

问题是我想断言 generate_cfg_thresh_map() 函数中设置的 max_eval_count 的值。由于该值是在全局变量中设置的，而不是从函数返回的，所以我无法在我的测试用例中断言该值。我无法使用函数中的 return，即根本不更改应用程序代码。

我该怎么做？即运行被测函数并检查函数为测试字符串设置的值，并根据函数设置的值断言单元测试用例。

Answer 1

引用 mock_open docs:

read_data is a string for the read(), readline(), and readlines() methods of the file handle to return. Calls to those methods will take data from read_data until it is depleted.

这意味着在迭代模拟文件对象时不会调用read_data。一个简单的解决方法是将 generate_cfg_thresh_map 函数的实现更改为：

def generate_cfg_thresh_map():
    ...
    try:
        with open ('/opt/config/pwr_thresh_cfg', 'r') as fh:
            <b>for line in fh.readlines():</b>
                ...

如果您不能更改函数，或者您可以增强 mock_open 返回的模拟对象：

Python 3

class ReportMonitor(unittest.TestCase):
    def test_generate_cfg_thresh_map(self):
        m = mock_open(read_data='ENTRY_THRESH_COUNT 200')
        m.return_value.__iter__ = lambda self: self
        m.return_value.__next__ = lambda self: next(iter(self.readline, ''))
        with patch('app.open', m):
            app.generate_cfg_thresh_map()
            assert app.max_eval_count == 200

Python 2

class ReportMonitor(unittest.TestCase):
    def test_generate_cfg_thresh_map(self):
        m = mock_open(read_data='ENTRY_THRESH_COUNT 200')
        m.return_value.__iter__ = lambda self: iter(self.readline, '')
        with patch('app.open', m):
            app.generate_cfg_thresh_map()
            assert app.max_eval_count == 200

致谢：Customizing unittest.mock.mock_open for iteration.

无法使用 mock_open() 在模拟函数中测试全局值

Unable to test a global value in a mocked function using mock_open()

python

python-2.7

pytest

python-mock

Python 3

Python 2