pythonunit-testingmockingnose

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

  • 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