利用Python中的mock库对Python代码进行模拟测试

#!/usr/bin/env python# -*- coding: utf-8 -*-from mymodule import RemovalService, UploadServiceimport mockimport unittestclass RemovalServiceTestCase(unittest.TestCase):
   
  @mock.patch('mymodule.os.path')
  @mock.patch('mymodule.os')
  def test_rm(self, mock_os, mock_path):
    # instantiate our service
    reference = RemovalService()    
    # set up the mock
    mock_path.isfile.return_value = False
     
    reference.rm("any path")    
    # test that the remove call was NOT called.
    self.assertFalse(mock_os.remove.called, "Failed to not remove the file if not present.")    
    # make the file 'exist'
    mock_path.isfile.return_value = True
     
    reference.rm("any path")
     
    mock_os.remove.assert_called_with("any path")   
    
class UploadServiceTestCase(unittest.TestCase):
 
  def test_upload_complete(self, mock_rm):
    # build our dependencies
    mock_removal_service = mock.create_autospec(RemovalService)
    reference = UploadService(mock_removal_service)    
    # call upload_complete, which should, in turn, call `rm`:
    reference.upload_complete("my uploaded file")    
    # test that it called the rm method
    mock_removal_service.rm.assert_called_with("my uploaded file")

在这个例子中，我们甚至不需要补充任何功能，只需创建一个带auto-spec方法的RemovalService类，然后将该实例注入到UploadService中对方法验证。

mock.create_autospec为类提供了一个同等功能实例。这意味着，实际上来说，在使用返回的实例进行交互的时候，如果使用了非法的方法将会引发异常。更具体地说，如果一个方法被调用时的参数数目不正确，将引发一个异常。这对于重构来说是非常重要。当一个库发生变化的时候，中断测试正是所期望的。如果不使用auto-spec，即使底层的实现已经破坏，我们的测试仍然会通过。

陷阱：mock.Mock和mock.MagicMock类

mock库包含两个重要的类mock.Mock和mock.MagicMock，大多数内部函数都是建立在这两个类之上的。在选择使用mock.Mock实例，mock.MagicMock实例或auto-spec方法的时候,通常倾向于选择使用 auto-spec方法，因为它能够对未来的变化保持测试的合理性。这是因为mock.Mock和mock.MagicMock会无视底层的API，接受所有的方法调用和参数赋值。比如下面这个用例：

class Target(object):
  def apply(value):
    return valuedef method(target, value):
  return target.apply(value)

class MethodTestCase(unittest.TestCase):
 
  def test_method(self):
    target = mock.Mock()
 
    method(target, "value")
 
    target.apply.assert_called_with("value")

class Target(object):
  def apply(value, are_you_sure):
    if are_you_sure:      return value    else:      return None

import facebookclass SimpleFacebook(object):
   
  def __init__(self, oauth_token):
    self.graph = facebook.GraphAPI(oauth_token)  def post_message(self, message):
    """Posts a message to the Facebook wall."""
    self.graph.put_object("me", "feed", message=message)

import facebookimport simple_facebookimport mockimport unittestclass SimpleFacebookTestCase(unittest.TestCase):
   
  @mock.patch.object(facebook.GraphAPI, 'put_object', autospec=True)
  def test_post_message(self, mock_put_object):
    sf = simple_facebook.SimpleFacebook("fake oauth token")
    sf.post_message("Hello World!")    # verify
    mock_put_object.assert_called_with(message="Hello World!")