[英]Mocking a Python class that is instantiated in method under test
我有一個受測試的系統(下面的類Printer
),它使用另一個類(下面的Class ContentContainer
)。 在一個方法(下面的方法retrieve_and_show_content
)中,實例化此類。 在這個方法的測試中(下面的方法test_printer_03
),我想實例化一個mock而不是真正的類。 但是,它不會像這樣工作。
我在這里讀到我應該更改名稱指向的對象與另一個。 看起來我要替換的對象的名稱只是ContentContainer
,而我實際替換的對象的名稱是TestMockClass.ContentContainer
。 這個觀察是否正確? 如果是這樣,我該如何更改? 如果我只是在patch語句中刪除前綴TestMockClass
,我會得到一個TypeError: Need a valid target to patch. You supplied: 'ContentContainer'
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()
運行此單元測試時,輸出為:
AssertionError:
Retrieved:
P03 says: Content from ContentContainer
Expected:
P03 says: Mocked content
兩件事情:
因為ContentContainer
現在與測試位於同一個文件中,所以實際上需要修補__main__.ContentContainer
:
@patch('__main__.ContentContainer')
因為ContentContainer
是一個類,並且您在該類的實例上調用content
,所以您實際上希望模擬該實例上的content
,而不是類。 因此,您需要執行以下操作: mock_cc.return_value.content.return_value = 'Mocked content'
(請注意其中的附加.return_value
以確保您正在.return_value
實例,而不是類)。 這是因為調用類會創建一個實例。 因此,實例是類上調用的返回值。
因此測試應如下所示:
@patch('__main__.ContentContainer')
def test_printer_03(self, mock_cc):
mock_cc.return_value.content.return_value = 'Mocked content'
...
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