Python Unit Test Patch Function - Avoid passing mocked function to test function

Question

I am trying to mock a python function similar to below. I am not doing anything with the mocked function except for the fact that it is used to return the mocked data in the called function. Is it possible for me to avoid passing in the variable (sum, in this case) to the test function?

# test_calculator.py

from unittest import TestCase
from unittest.mock import patch

class TestCalculator(TestCase):
    @patch('calculator.Calculator.sum', return_value=9)
    def test_sum(self, sum):
        self.assertEqual(sum(2,3), 9)

What are you trying to do exactly? From looking at the documentation of patch it seems to expect classes as inputs, not functions. Am I missing something? — Tasos Papastylianou
– Tasos Papastylianou, Commented Feb 27, 2020 at 21:42
I believe functions can be mocked. This is the example that I was following - semaphoreci.com/community/tutorials/… — Punter Vicky
– Punter Vicky, Commented Feb 27, 2020 at 21:48
Why are you mocking anything? All you are doing here is testing that your mock indeed returns 9. That is, you've written a more verbose form of self.assertEqual(9, 9). — chepner
– chepner, Commented Feb 27, 2020 at 22:10
I don't have time to test in code, but from the documentation of patch it seems that, if you don't specify the new argument, then you have to do it as above. If you specify the new argument (presumably pointing to another class or function) then you can skip the second argument in the decorated function signature. I do not know if you can specify such a new function on the spot via a lambda though. — Tasos Papastylianou
– Tasos Papastylianou, Commented Feb 27, 2020 at 23:47

theY4Kman · Accepted Answer · 2020-02-29 21:52:42Z

2

unittest.mock.patch can also be used as a context manager, if simply avoiding sum in the parameters is desired

class TestCalculator(TestCase):
    def test_sum(self):
        with patch('calculator.Calculator.sum', return_value=9) as sum:
            self.assertEqual(sum(2, 3), 9)

answered Feb 29, 2020 at 21:52

theY4Kman

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