Why python mock patch doesn't work?
I have two files
spike.py
class T1(object):
def foo(self, afd):
return "foo"
def get_foo(self):
return self.foo(1)
def bar():
return "bar"
test_spike.py:
from unittest import TestCase
import unittest
from mock import patch, MagicMock
from spike import T1, bar
class TestStuff(TestCase):
@patch('spike.T1.foo', MagicMock(return_value='patched'))
def test_foo(self):
foo = T1().get_foo()
self.assertEqual('patched', foo)
@patch('spike.bar')
def test_bar(self, mock_obj):
mock_obj.return_value = 'patched'
bar = bar()
self.assertEqual('patched', bar)
if __name__ == "__main__":
unittest.main()
When I run python test_spike.py
, the first test case would pass, but the second would fail.
and I switch to use nosetests test_spike.py
, then both two are failed.
I don't understand how this happened? These cases supposed to pass all.
Solution 1:
Access bar
using spike.bar
. Imported bar
is not affected by mock.patch
.
from unittest import TestCase
import unittest
from mock import patch, MagicMock
from spike import T1
import spike # <----
class TestShit(TestCase):
@patch('spike.T1.foo', MagicMock(return_value='patched'))
def test_foo(self):
foo = T1().get_foo()
self.assertEqual('patched', foo)
@patch('spike.bar')
def test_bar(self, mock_obj):
mock_obj.return_value = 'patched'
bar = spike.bar() # <-----
self.assertEqual('patched', bar)
if __name__ == "__main__":
unittest.main()
Solution 2:
For test_foo you are not using patch correctly. You should be using it like this:
class TestFoo(TestCase):
@patch.object(T1, 'foo', MagicMock(return_value='patched'))
def test_foo(self):
foo = T1().get_foo()
self.assertEqual('patched', foo)
that gives me:
nosetests test_spike.py
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK
Now the second example does not work because you import bar function (get a reference to it) and then try to mock it. When you mock something you can't change what your variables hold (reference to original function). To fix this you should use @falsetru suggested method like:
from unittest import TestCase
import unittest
from mock import patch
import spike
class TestFoo(TestCase):
@patch('spike.bar')
def test_bar(self, mock_obj):
mock_obj.return_value = 'patched'
value = spike.bar()
self.assertEqual('patched', value)
if __name__ == "__main__":
unittest.main()
this gives me:
python test_spike.py
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK
But when I try to run it with nose I get:
nosetests test_spike.py
F
======================================================================
FAIL: test_bar (src.test_spike.TestFoo)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/zilva/envs/test/local/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched
return func(*args, **keywargs)
File "/home/zilva/git/test/src/test_spike.py", line 11, in test_bar
self.assertEqual('patched', value)
AssertionError: 'patched' != 'bar'
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)
This happends because I am patching not in the right place. My directory structure is:
test/
└── src/
├── spike.py
├── test_spike.py
└── __init__.py
and I run tests from src directory so I should be patching using path from project root directory like:
@patch('src.spike.bar')
and this would give me:
nosetests test_spike.py
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK
or if I am at test directory:
nosetests src/test_spike.py
.
----------------------------------------------------------------------
Ran 1 test in 0.001s
OK