python - Using mock patch to mock an instance method

Question

I'm trying to mock something while testing a Django app using the imaginatively named Mock testing library. I can't seem to quite get it to work, I'm trying to do this:

models.py

from somelib import FooClass

class Promotion(models.Model):
    foo = models.ForeignKey(FooClass)
    def bar(self):
       print "Do something I don't want!"


test.py

class ViewsDoSomething(TestCase):
    view = 'my_app.views.do_something'

    def test_enter_promotion(self):
        @patch.object(my_app.models.FooClass, 'bar')
        def fake_bar(self, mock_my_method):
            print "Do something I want!"
            return True

        self.client.get(reverse(view))

What am I doing wrong?

bar is in fact an "instance method," and its only parameter is self. To be a class method, it would need to be parameterized with cls, and would be callable as Promotion.foo(). — cavaunpeu
Patchable object needs to be quoted like this: @patch.object('my_app.models.FooClass', 'bar') — Lasma
@cavaunpeu - not (just) parameterized with cls, but more importantly (since self and cls don't mean anything special in python), decorated with @classmethod — dwanderson

storm_m2138 storm_m2138 · Accepted Answer · 2015-12-30T17:56:52

To add onto Kit's answer, specifying a 3rd argument to patch.object() allows the mocked object/method to be specified. Otherwise, a default MagicMock object is used.

    def fake_bar(self):
        print "Do something I want!"
        return True

    @patch.object(my_app.models.FooClass, 'bar', fake_bar)
    def test_enter_promotion(self):
        self.client.get(reverse(view))
        # Do something I want!

Note that, if you specify the mocking object, then the default MagicMock() is no longer passed into the patched object -- e.g. no longer:

def test_enter_promotion(self, mock_method):

but instead:

def test_enter_promotion(self):

http://www.voidspace.org.uk/python/mock/patch.html#patch-object

python - Using mock patch to mock an instance method

2 Answers