Python unittest模拟方法在另一个模块中调用时出错

Question

This is my probject structure, and this problem is a MCVE.

• wrx_test
  • use_mock
  • init .py
  • A.py
  • B.py
  • use_mock.py

A.py

def do_something():
    print 'a i do something'
    return 10

B.py

from wrx_test.use_mock.A import do_something
class B(object):
    def b_do_something(self):
        x = do_something()
        print x
        return x

use_mock.py

from mock import patch
from unittest import TestCase

from wrx_test.use_mock.B import B


class TestUseMock(TestCase):
    @patch('wrx_test.use_mock.A.do_something')
    def test_use_mock(self, mock_do_something):
        from wrx_test.use_mock.A import do_something

        mock_do_something.return_value = 4
        print do_something()
        B().b_do_something()

In use_mock.py i set the mocked method return_value equal 4, but it doesn't work as excepted. How can i make the mocked method A.do_something work correctly in module B, and i wonder now the reason.

result

a i do something
10 

Answer 1

I think the way mock works is that you designate a function in a module to be replaced by your mock when this function is used in another call. Example: patch('A.do_something) would mean that if you test a function that internally calls A.do_something(), it will be replaced inside that call. But here you're directly executing that function. I also don't see any useful case for doing this. If you want to call the mock directly, do: mock_do_something()