Python 3.3+unittestfunction

unittest.mock.patch()

mocks

A decorator and a context manager that replace objects with mocks during a test. They isolate the code under test from its external dependencies.

Syntax

from unittest.mock import patch
@patch('module.ClassName')
def test(self, mock_cls): ...

with patch('module.func') as m: ...

The classic trap is patching the wrong place: patch the name where it is looked up, not where it was defined — if the module under test imported the name into its own namespace, patching the original module has no effect. With several stacked decorators the mocks arrive bottom-up, so the @patch closest to the function maps to the first parameter.

Examples

from unittest.mock import patch
import unittest
class Tests(unittest.TestCase):
    @patch('builtins.input', return_value='42')
    def test_input(self, mock_input):
        self.assertEqual(input(), '42')
        mock_input.assert_called_once()

See also

Common errors

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