我該如何嘲笑open（...）。write（）而沒有得到'沒有這樣的文件或目錄'的錯誤？

Question

我根據我的解決方案：

• How do I mock an open used in a with statement (using the Mock framework in Python)?，
• AttributeError: <module '__main__' from [..] does not have the attribute 'open'，
• http://www.voidspace.org.uk/python/mock/helpers.html#mock.mock_open

我有一個類，這是我可以實例，其寫入文件。我試圖測試它，但我有問題嘲笑open()。我用以下爲最小的一段代碼，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 

當我運行它，我得到以下錯誤：

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' 

我怎麼能嘲笑的open（），使它只是返回一個file_pointer，並且不會嘗試與文件系統進行交互？

Answer 1

莫克builtins.open（或module.open，module =包含WriteData模塊名稱）與mock_open：

import builtins 

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('builtins.open', unittest.mock.mock_open()) as m: 
      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') # fixed 
     m.assert_called_once_with('/my/path/not/exists/output.text', 'w+') 
     handle = m() 
     handle.write.assert_called_once_with('Hello, Foo!')