为什么我不能用 unittest.mock.patch 有效地模拟功能？

Question

I'm trying to write UT for function with other function mocked. Both lies in the same module. It appears that unittest.mock.patch() call passes without error but doesn't mock anything so I'm getting exception in the example code. So, my question is: How to mock foo with unittest.mock.patch ?

import unittest
import unittest.mock

def foo():
        raise Exception("not implemented")

def bar():
        foo()

class UT(unittest.TestCase):

        def testBar(self):
                with unittest.mock.patch('mock_test.foo',spec=True) as mock_foo:
                        bar()    # <- original foo is called here

unittest.main()

Answer 1

Here is a way to use unittest.mock.patch and patch the foo returns. See the comments in the example:

import unittest
from unittest.mock import patch


def foo():
        raise Exception("Not implemented")


def bar():
        return foo()


class UT(unittest.TestCase):

        def testBar(self):
            # foo is mocked to raise a ValueError and catch it during the test
            with patch('__main__.foo', side_effect=ValueError):
                with self.assertRaises(ValueError):
                    bar()

            # foo is mocked to raise and exception and catch it during the test
            with patch('__main__.foo', side_effect=Exception):
                with self.assertRaises(Exception):
                    bar()

            # foo is mocked to return 1
            with patch('__main__.foo', return_value=1):
                self.assertEqual(bar(), 1, "Should be equal to 1")

            # foo is mocked to return an object
            with patch('__main__.foo', return_value={}):
                self.assertIsInstance(bar(), dict, "Should be an instance of dict")


unittest.main()

Output:

.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK

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