Python如何在单元测试中给对象打补丁

from unittest.mock import patch
import example

@patch('example.func')
def test1(x, mock_func):
  example.func(x)    # Uses patched example.func
  mock_func.assert_called_with(x)

with patch('example.func') as mock_func:
  example.func(x)   # Uses patched example.func
  mock_func.assert_called_with(x)

p = patch('example.func')
mock_func = p.start()
example.func(x)
mock_func.assert_called_with(x)
p.stop()

@patch('example.func1')
@patch('example.func2')
@patch('example.func3')
def test1(mock1, mock2, mock3):
  ...

def test2():
  with patch('example.patch1') as mock1, \
     patch('example.patch2') as mock2, \
     patch('example.patch3') as mock3:
  ...

>>> x = 42
>>> with patch('__main__.x'):
...   print(x)
...
<MagicMock name='x' id='4314230032'>
>>> x
42
>>>

>>> x
42
>>> with patch('__main__.x', 'patched_value'):
...   print(x)
...
patched_value
>>> x
42
>>>

>>> from unittest.mock import MagicMock
>>> m = MagicMock(return_value = 10)
>>> m(1, 2, debug=True)
10
>>> m.assert_called_with(1, 2, debug=True)
>>> m.assert_called_with(1, 2)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File ".../unittest/mock.py", line 726, in assert_called_with
  raise AssertionError(msg)
AssertionError: Expected call: mock(1, 2)
Actual call: mock(1, 2, debug=True)
>>>

>>> m.upper.return_value = 'HELLO'
>>> m.upper('hello')
'HELLO'
>>> assert m.upper.called

>>> m.split.return_value = ['hello', 'world']
>>> m.split('hello world')
['hello', 'world']
>>> m.split.assert_called_with('hello world')
>>>

>>> m['blah']
<MagicMock name='mock.__getitem__()' id='4314412048'>
>>> m.__getitem__.called
True
>>> m.__getitem__.assert_called_with('blah')
>>>

# example.py
from urllib.request import urlopen
import csv

def dowprices():
  u = urlopen('http://finance.yahoo.com/d/quotes.csv?s=@^DJI&f=sl1')
  lines = (line.decode('utf-8') for line in u)
  rows = (row for row in csv.reader(lines) if len(row) == 2)
  prices = { name:float(price) for name, price in rows }
  return prices

import unittest
from unittest.mock import patch
import io
import example

sample_data = io.BytesIO(b'''\
"IBM",91.1\r
"AA",13.25\r
"MSFT",27.72\r
\r
''')

class Tests(unittest.TestCase):
  @patch('example.urlopen', return_value=sample_data)
  def test_dowprices(self, mock_urlopen):
    p = example.dowprices()
    self.assertTrue(mock_urlopen.called)
    self.assertEqual(p,
             {'IBM': 91.1,
             'AA': 13.25,
             'MSFT' : 27.72})

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