Argthtjtr

I'm trying to patch a function defined in a different module from the module containing the testing code. If the function and its test are defined in the same module, I've found that the following works:

import unittest

from mock import patch





def foo():

    return 'bar'





class FooTest(unittest.TestCase):

    @patch('__main__.foo')

    def test_foo(self, mock_foo):

        mock_foo.return_value = 'baz'



        foo()



        mock_foo.assert_called()





if __name__ == "__main__":

    unittest.main()

Moreover, if I drop into the debugger in test function just before the foo() call, I see that foo is a MagicMock instance, and that if I call it, it returns 'baz' (not 'bar') as expected.

I've tried to adapt this somewhat as follows. In the same directory, I've written a foo_module.py containing just the definition of foo():

def foo():

    return 'bar'

and I've imported this function in the testing module and changed the patch() argument from __main__.foo to foo_module.foo:

import unittest

from mock import patch

from foo_module import foo





class FooTest(unittest.TestCase):

    @patch('foo_module.foo')

    def test_foo(self, mock_foo):

        mock_foo.return_value = 'baz'



        foo()



        mock_foo.assert_called()





if __name__ == "__main__":

    unittest.main()

However, if I try to run this, I get an AssertionError because the mock_foo was not called:

$ python use_patch.py

F

======================================================================

FAIL: test_foo (__main__.FooTest)

----------------------------------------------------------------------

Traceback (most recent call last):

  File "/Users/kupeek/Documents/Scratch/venv/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched

    return func(*args, **keywargs)

  File "use_patch.py", line 13, in test_foo

    mock_foo.assert_called()

  File "/Users/kupeek/Documents/Scratch/venv/lib/python2.7/site-packages/mock/mock.py", line 906, in assert_called

    raise AssertionError(msg)

AssertionError: Expected 'foo' to have been called.



----------------------------------------------------------------------

Ran 1 test in 0.001s



FAILED (failures=1)

Indeed now if I drop into the debugger, foo is an ordinary function and no longer a MagicMock instance, and it returns 'bar' instead of 'baz':

$ python use_patch.py

> /Users/kupeek/Documents/Scratch/use_patch.py(11)test_foo()

     10         import ipdb; ipdb.set_trace()

---> 11         foo()

     12 



ipdb> foo

<function foo at 0x107347410>

ipdb> mock_foo

<MagicMock name='foo' id='4429017168'>

ipdb> foo()

'bar'

Any idea why this is not working? I've consulted the docs (https://docs.python.org/3/library/unittest.mock.html#unittest.mock.patch) but to no avail so far...

I managed to get the example to work by, instead of from foo_module import foo and calling foo(), doing import foo_module followed by foo_module.foo():

import unittest

from mock import patch

import foo_module





class FooTest(unittest.TestCase):

    @patch('foo_module.foo')

    def test_foo(self, mock_foo):

        mock_foo.return_value = 'baz'



        foo_module.foo()



        mock_foo.assert_called()





if __name__ == "__main__":

    unittest.main()

Basically the patch() decorator determines a target and an attribute, and internally replaces that attribute by a mock instance, along the lines of

setattr(target, attribute, MagicMock())

In the original example, the foo() function was being imported directly and was not an 'attribute' of the foo_module, so the patcher was not patching the intended object.