How to correctly use pytest mocker to patch a function?

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I’ve worked with pytest mocker quite a bit, and the key to using it correctly is ensuring you’re patching the right function with the correct path. Here’s a simple example of patching with return_value to override a function’s output:

:small_blue_diamond: Patching with a return_value to Simulate a Fixed Result:

You can make a function return a fixed value, regardless of its input:

import pytest

def sum(a, b):
    return a + b

def test_sum1(mocker):
    mocker.patch(__name__ + ".sum", return_value=9)
    assert sum(2, 3) == 9  # This will pass because 'sum' always returns 9 now

Here, pytest mocker ensures sum() always returns 9, making the test predictable.