Python 如何模拟open（…）.write（）而不获得'；没有这样的文件或目录'；错误？

我的解决方案基于：

• ,

我有一个可以实例化的类，它可以写入文件。我正在尝试测试它，但在模拟

open（）

时遇到问题。我使用下面的代码作为最小的一段代码，它可以

import os
import unittest
from unittest.mock import mock_open, patch

__author__ = 'drews'


class MockPathExists(object):
    def __init__(self, return_value):
        self.received_args = None
        self.return_value = return_value

    def __call__(self, *args, **kwargs):
        self.received_args = args
        return self.return_value


class WriteData:
    def __init__(self, dir, name='World'):
        self.name = name
        self.dir = dir

    def dump(self):
        if os.path.exists(self.dir):
            with open('{0}/output.text'.format(self.dir), 'w+') as fp:
                fp.write('Hello, {0}!'.format(self.name))


class TestListWindowsPasswords(unittest.TestCase):
    def setUp(self):
        self._orig_pathexists = os.path.exists
        os.path.exists = MockPathExists(True)

    def test_dump(self):
        m = mock_open()
        with patch.object(WriteData, 'open', m, create=True):
            data_writer = WriteData(
                dir='/my/path/not/exists',
                name='Foo'
            )
            data_writer.dump()

        self.assertEqual(os.path.exists.received_args[0], '/my/path/not/exists/output.text')
        m.assert_called_once_with('/my/path/not/exists/output.text', 'w+')
        handle = m()
        handle.write.assert_called_once_with('Hello, Foo!')



    def tearDown(self):
        os.path.exists = self._orig_pathexists

当我运行此操作时，会出现以下错误：

Error
Traceback (most recent call last):
  File "/Users/drews/Development/tool/tests/test_mockopen.py", line 41, in test_dump
    data_writer.dump()
  File "/Users/drews/Development/tool/tests/test_mockopen.py", line 25, in dump
    with open('{0}/output.text'.format(self.dir), 'w+') as fp:
FileNotFoundError: [Errno 2] No such file or directory: '/my/path/not/exists/output.text'

---

如何才能模拟open（），使其只返回一个文件指针，而不尝试与文件系统进行交互？

mock

builtins.open

（或

module.open

，

module

=包含

WriteData

的模块名称）具有：

---

您可以使用_uenter _; magic方法模拟以下情况：

from unittest.mock import patch, MagicMock, call, mock_open

@patch('os')
@patch('builtins.open', new_callable=mock_open())
def test_dump(self, mock_open_file, mock_os):
    data_writer = WriteData(dir='/my/path/not/exists', name='Foo')

    mock_os.path.exists.assert_called_once_with('/my/path/not/exists')
    mock_open_file.assert_called_once_with('/my/path/not/exists/output.text', 'w+')
    mock_open_file.return_value.__enter__().write.assert_called_once_with('Hello, Foo!')

---

希望这有帮助

我的问题是没有使用“builtins.open”。谢谢测试转储的第一行可能是reduntant？“m=mock_open（）@yaroslavinkitenko，你说得对。相应地更新了答案。非常感谢。

from unittest.mock import patch, MagicMock, call, mock_open

@patch('os')
@patch('builtins.open', new_callable=mock_open())
def test_dump(self, mock_open_file, mock_os):
    data_writer = WriteData(dir='/my/path/not/exists', name='Foo')

    mock_os.path.exists.assert_called_once_with('/my/path/not/exists')
    mock_open_file.assert_called_once_with('/my/path/not/exists/output.text', 'w+')
    mock_open_file.return_value.__enter__().write.assert_called_once_with('Hello, Foo!')