Using unittest.mock

https://docs.python.org/3/library/unittest.mock.html

https://realpython.com/python-mock-library/
Understanding the Python Mock Object Library

INTRODUCTION

unittest.mock is a library for testing in Python (Py3.3+). It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used.

Mock is a flexible mock object intended to replace the use of stubs and test doubles throughout your code.

MagicMock is a subclass of Mock with all the magic methods pre-created and ready to use.

Mock can create arbitrary attributes on the fly.

from unittest.mock import Mock

mock = Mock()

print(mock)
print(mock.some_attribute)
print(mock.do_something())

# <Mock id='140138960515368'>
# <Mock name='mock.some_attribute' id='140138960515592'>
# <Mock name='mock.do_something()' id='140138958324288'>

from unittest.mock import MagicMock

class ProductionClass: pass

thing = ProductionClass()
thing.method = MagicMock(return_value=3)
thing.method(3, 4, 5, key='value')   # returns 3

thing.method.assert_called_with(10, key='x')
thing.method(10, key='y')
# AssertionError: expected call not found.