Mocking Functions in Python

When writing unit/integration tests in Python, the general pattern is to use unittest.mock.patch. This is great, but you need to be careful about the namespaces. 

# tests.py
from path.to.funcB
from unittest.mock import patch
# assume funcB calls the somepypipackage.funcA

@patch("somepypipackage.funcA")
def test_funcB(funcA):
    funcA.return_value = 3
    assert funcB() == "correct_value"

This will only mock funcA calls within the scope of tests.py. funcB is in a different namespace so calls funcB makes to funcA will not be mocked To ensure funcA calls are mocked properly specifically write the namespace it needs to be mocked within

# tests.py
from path.to.funcBfile import funcB
from unittest.mock import patch

# assume funcB calls the somepypipackage.funcA

@patch("path.to.funcBfile.funcA")
def test_funcB(funcA):
    funcA.return_value = 3
    assert funcB() == "correct_value"

Tags: #python