CODEWITHSUNDEEP
pythonunit-testingmocking
Nova
Nova

Reputation: 2666

Mocking a class method that is used via an instance

I'm trying to patch a class method using mock as described in the documentation. The Mock object itself works fine, but its methods don't: For example, their attributes like call_count aren't updated, even though the method_calls attribute of the class Mock object is. More importantly, their return_value attribute is ignored: 

class Lib:
    """In my actual program, a module that I import"""
    def method(self):
        return "real"

class User:
    """The class I want to test"""
    def run(self):
        l = Lib()
        return l.method()

with patch("__main__.Lib") as mock:
    #mock.return_value = "bla" # This works
    mock.method.return_value = "mock"
    u = User()
    print(u.run())

>>> 
mock
<MagicMock name='Lib().method()' id='39868624'>

What am I doing wrong here?

EDIT: Passing a class Mock via the constructor doesn't work either, so this is not really related to the patch function.

Upvotes: 12

Views: 9084

Answers (3)

guettli
guettli

Reputation: 27806

I mock classmethods like this:

def raiser(*args, **kwargs):
    raise forms.ValidationError('foo')
with mock.patch.object(mylib.Commands, 'my_class_method', classmethod(raiser)):
    response=self.admin_client.get(url, data=dict(term='+1000'))

Upvotes: 1

Nova
Nova

Reputation: 2666

I have found my error: In order to configure the methods of my mock's instances, I have to use mock().method instead of mock.method.

class Lib:
    """In my actual program, a module that I import"""
    def method(self):
        return "real"

class User:
    """The class I want to test"""
    def run(self):
        l = Lib()
        return l.method()

with patch("__main__.Lib") as mock:
    #mock.return_value = "bla" # This works
    mock().method.return_value = "mock"
    u = User()
    print(u.run())

Upvotes: 18

John
John

Reputation: 13699

from mock import *

class Lib:
    """In my actual program, a module that I import"""
    def method(self):
        return "real"

class User:
    """The class I want to test"""
    def run(self, m):

        return m.method()

with patch("__main__.Lib") as mock:
    #mock.return_value = "bla" # This works
    mock.method.return_value = "mock"

    print User().run(mock)

Upvotes: 1

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