嘲讽在被测方法中实例化的Python类

Question

我有一个被测系统（下面的类Printer），它使用另一个类（下面的类ContentContainer）。在一种方法（下面的方法retrieve_and_show_content）中，这个类被实例化。在这个方法的测试中（下面的方法test_printer_03），我想实例化一个模拟而不是真实的类。但是，它不能这样工作。

我读here，我应该改变名称与另一个指向的对象。看起来我想要替换的对象的名称只是ContentContainer，而我实际替换的对象的名称是TestMockClass.ContentContainer。这个观察是否正确？如果是这样，我该如何改变这一点？如果我只是在补丁语句中删除前缀TestMockClass，我会得到一个TypeError: Need a valid target to patch. You supplied: 'ContentContainer'。

#TestMockClass.py 
import unittest 
from mock import Mock, patch 

class Printer(): 
    def __init__(self, name, cc): 
     self.name = name 
     self.cc = cc 
    def show_content(self): 
     text = '{0} says: {1}'.format(self.name, self.cc.content()) 
     return text 
    def retrieve_and_show_content(self): 
     cc_tmp = ContentContainer() 
     text = '{0} says: {1}'.format(self.name, cc_tmp.content()) 
     return text 

class ContentContainer(): 
    def __init__(self): 
     self.method_counter() 
    def content(self): 
     return 'Content from ContentContainer' 
    def method_counter(self): 
     pass 

class Test(unittest.TestCase): 

    '''No mocking''' 
    def test_printer_01(self): 
     cc = ContentContainer() 
     sut = Printer('P01', cc) 
     result = sut.show_content() 
     expected_result = 'P01 says: Content from ContentContainer' 
     self.assertEqual(result, expected_result, 
         msg = '\nRetrieved:\n{0} \nExpected:\n{1}'.format(result, expected_result)) 
     result = sut.retrieve_and_show_content() 
     expected_result = 'P01 says: Content from ContentContainer' 
     self.assertEqual(result, expected_result, 
         msg = '\nRetrieved:\n{0} \nExpected:\n{1}'.format(result, expected_result)) 

    '''Create a mock object, which is the input of the method under test''' 
    def test_printer_02(self): 
     mock_cc = Mock() 
     mock_cc.content.return_value = 'Mocked content' 
     sut = Printer('P02', mock_cc) 
     result = sut.show_content() 
     expected_result = 'P02 says: Mocked content' 
     self.assertEqual(result, expected_result, 
         msg = '\nRetrieved:\n{0} \nExpected:\n{1}'.format(result, expected_result)) 
     self.assertFalse(mock_cc.method_counter.called, 'Method method_counter shall not be called') 

    '''Create a mock class, which is instantiated inside the method under test''' 
    @patch('TestMockClass.ContentContainer') 
    def test_printer_03(self, mock_cc): 
     mock_cc.content.return_value = 'Mocked content' 
     sut = Printer('P03', mock_cc) 
     result = sut.retrieve_and_show_content() 
     expected_result = 'P03 says: Mocked content' 
     self.assertEqual(result, expected_result, 
         msg = '\nRetrieved:\n{0} \nExpected:\n{1}'.format(result, expected_result)) 
     self.assertFalse(mock_cc.method_counter.called, 'Method method_counter shall not be called') 

if __name__ == "__main__": 
    unittest.main() 

当这个单元测试运行时，输出为：

AssertionError: 
Retrieved: 
P03 says: Content from ContentContainer 
Expected: 
P03 says: Mocked content 

Answer 1

两件事情：

1. 因为ContentContainer现在是在同一个文件作为测试，你确实需要patch __main__.ContentContainer：

   @patch('__main__.ContentContainer') 
   

2. 因为ContentContainer是一类，而你在该类的实例上调用content，所以实际上你希望在该实例上模拟content，而不是在类上。因此，您需要：mock_cc.return_value.content.return_value = 'Mocked content'（请注意其中的.return_value以确保您嘲笑实例，而不是课程）。这是因为调用一个类创建一个实例。所以，这个实例就是这个类的调用的返回值。

试验应如此模样：

@patch('__main__.ContentContainer') 
def test_printer_03(self, mock_cc): 
    mock_cc.return_value.content.return_value = 'Mocked content' 
    ...