Python @patch not working

Question

I am trying to test a method that within it creates an instance of another class, I am attempting to mock the creation of the inner class... That is not working for me. I tried replicating the problem to a simplified case - and still no go. Here is the simplified case:

I have a directory named pymock with a __init__.py in it. Other than that there are these 3 files:

foo.py

#!/usr/bin/python
class Foo(object):
    def foo1(self):
        return 1

goo.py

#!/usr/bin/python
from foo import Foo


class Goo(object):
    def goo1(self):
        f = Foo()
        return f.foo1()

goo_test.py

#!/usr/bin/python
from mock import patch, Mock
from nose.tools import assert_equal

from goo import Goo


class TestGoo(object):
    def setup(self):
        self.goo = Goo()

    @patch('pymock.foo.Foo', autospec=True)
    def test_goo1(self, foo1_mock):
        foo_instance = Mock()
        foo1_mock.return_value = foo_instance
        foo_instance.foo1.return_value = 11
        assert_equal(11, self.goo.goo1())

Thanks in advance!

chepner · Accepted Answer · 2015-09-08 15:37:10Z

28

You need to patch the name that goo is using.

@patch('pymock.goo.Foo', autospec=True)

edited Sep 8, 2015 at 15:37

answered Sep 8, 2015 at 15:18

chepner

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7 Comments

Uri Shalit Over a year ago

Doesn't seem right. Anyway I tried - got ImportError: No module named goo

chepner Over a year ago

I wasn't sure if it needed the pymock as `well.

chepner Over a year ago

mock.patch replaces the object that a name refers to, and pymock.foo.Foo is the name that your test module uses to access that function. Python has no true global variables; the goo module has its own reference to foo.Foo that its functions use, so that is the name you need to patch.

Mojowen Over a year ago

Oh my jesus I was stuck on this for a day and this clicked it for me - don't patch the source of the method: @patch('djang.some.lib.get_template') - patch where it's being used @patch('my_project.email.get_template'). Game changer.

SeeDerekEngineer Over a year ago

@chepner, your third comment should be part of the answer, imo. It does a great job at explaining why the answer is correct, as it applies to methods as well.

|

cberenik · Accepted Answer · 2015-09-08 16:17:52Z

15

Basically it's how you import functions/classes. In goo.py you've imported Foo directly. So goo.py has it's own reference to Foo, so your patch will have to be: @patch('pymock.goo.Foo', autospec=True)

But if goo.py looked like this:

#!/usr/bin/python
import foo


class Goo(object):
    def goo1(self):
        f = foo.Foo()
        return f.foo1()

the patch in your question would work since goo.py doesn't have a direct reference to Foo

answered Sep 8, 2015 at 16:17

cberenik

1514 bronze badges

1 Comment

SeeDerekEngineer Over a year ago

Fantastic explanation of the why, @cberenik. You helped me out of a pinch here, so thanks.

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