How to mock objects methods return value

Question

what I currently have is:

def some_method():
    some_obj = some_other_method()
    # This is what I want to mock return value of:
    some_obj.some_obj_some_method()

@patch('some_package.some_other_method')
def test_some_stuff(some_other_method_patch):
    some_other_method_patch.return_value = SomeObject()

How could I get about setting some_obj.some_obj_some_method() return value to False?

Answer 1

patch('some_package.some_other_method') will replace the function some_other_method with a Mock. Now you need to replace the return value of the method some_obj_some_method of this mock:

mock.return_value.some_obj_some_method.return_value = False

The complete example:

# some_package.py

class SomeObject:
    def some_obj_some_method(self):
        raise RuntimeError()


def some_other_method():
    return SomeObject()


def some_method():
    some_obj = some_other_method()
    # This is what you want to mock return value of:
    return some_obj.some_obj_some_method()

Test:

from unittest.mock import patch
from some_package import SomeObject, some_method

@patch('some_package.some_other_method')
def test_some_stuff(function_mock):
    function_mock.return_value.some_obj_some_method.return_value = False
    assert not some_method()

The test will pass as is, will raise a RuntimeError without patching and fail the assertion without the line function_mock.return_value.some_obj_some_method.return_value = False because some_method will only return a Mock that is never False.

Answer 2

You can use patch.object

import mock
import some_obj
@mock.patch.object(some_obj, "some_obj_some_method")
def test_some_stuff(mock_some_obj_some_method):
    mock_some_obj_some_method.return_value = False