Python Mock Multiple Calls with Different Results

Question

I want to be able to have multiple calls to a particular attribute function return a different result for each successive call.

In the below example, I would like increment to return 5 on its first call and then 10 on its second call.

Ex:

import mock

class A:
    def __init__(self):
        self.size = 0
    def increment(self, amount):
        self.size += amount
        return amount

@mock.patch("A.increment")
def test_method(self, mock_increment):
    def diff_inc(*args):
        def next_inc(*args):
            #I don't know what belongs in __some_obj__
            some_obj.side_effect = next_inc
            return 10
        return 5

    mock_increment.side_effect = diff_inc

The below page has almost everything that I need except that it assumes that the caller would be an object named "mock", but this can't be assumed.

http://mock.readthedocs.org/en/latest/examples.html#multiple-calls-with-different-effects

Answer 1

You can just pass an iterable to side effect and have it iterate through the list of values for each call you make.

@mock.patch("A.increment")
def test_method(self, mock_increment):
    mock_increment.side_effect = [5,10]
    self.assertEqual(mock_increment(), 5)
    self.assertEqual(mock_increment(), 10)

Answer 2

I tested and this should work

import mock

...
...

@mock.patch.object(ClassB, 'method_2')
@mock.patch.object(ClassA, 'method_1')
def test_same_method_multi_return_value(self, method_1, method_2):
    # type: () -> None

    method_1.return_value = 'Static value'
    method_1.side_effect = [
        'Value called by first time'
        'Value called by second time'
        '...'
    ]

Version

https://mock.readthedocs.io/en/latest/
mock>=2.0.0,<3.0

Answer 3

I think the popping values off of a list method will be more straightforward. The below example works for the test you wanted to perform.

Also, I've had a difficult time with the mock library before and have found that the mock.patch.object() method was typically easier to use.

import unittest
import mock


class A:
    def __init__(self):
        self.size = 0

    def increment(self, amount):
        self.size += amount
        return amount

incr_return_values = [5, 10]


def square_func(*args):
    return incr_return_values.pop(0)


class TestMock(unittest.TestCase):

    @mock.patch.object(A, 'increment')
    def test_mock(self, A):
        A.increment.side_effect = square_func

        self.assertEqual(A.increment(1), 5)
        self.assertEqual(A.increment(-20), 10)