[PYTHON] I tried to summarize the frequently used implementation method of pytest-mock

I checked how to use pytest-mock, so make a note Since it is troublesome to check the use cases that are likely to be used in the future, I summarized them. It's an article I wrote in a day after I checked pytest, so I think there are various excesses and deficiencies, but if I find a better way, I will update it as needed.

About pytest and pytest-mock

It is one of the libraries used when implementing python test code. Please refer to the official website for details.

pytest https://docs.pytest.org/en/latest/index.html

pytest-mock https://pypi.org/project/pytest-mock/

Method used for explanation

The following hoge method is the test target.

from mailer import Mailer

#example messages
# ['1st text', 'Second text']
def hoge(messages):
    try:
        #Send as many emails as there are messages
        for message in messages:
          has_error = Mailer.send(message)
          if has_error:
            #1 is returned when an error occurs
            return 1

        #Returns 0 at the end of normal
        return 0
    except Exception as e:
        #2 is returned when an exception occurs
        return 2

The version used at the time of writing this article is as follows.

• python 3.8.5
• pytest 6.1.1
• pytest-mock 3.3.1

Replace Mailer.send with a mock

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # Mailer.Replace send with mock
    mailer_mock = mocker.patch.object(Mailer, 'send')

    messages = ['1st text', 'Second text']

    #Mailer above.Since send is a mock, even if you execute hoge, it is a real Mailer.send will not be executed
    assert hoge(messages) == 0

I want to verify the number of calls

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # Mailer.Replace send with mock
    mailer_mock = mocker.patch.object(Mailer, 'send')

    messages = ['1st text', 'Second text']
    assert hoge(messages) == 0

    # Mailer.You can see that send is called twice
    assert mailer_mock.call_count == 2

I want to verify that it is not called

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # Mailer.Replace send with mock
    mailer_mock = mocker.patch.object(Mailer, 'send')

    #Since messages are empty, Mailer. prevent send from being called
    messages = []
    assert hoge(messages) == 0

    # Mailer.Verify that send is not called
    mailer_mock.assert_not_called()

I want to verify the parameters

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # Mailer.Replace send with mock
    mailer_mock = mocker.patch.object(Mailer, 'send')

    messages = ['1st text', 'Second text']
    assert hoge(messages) == 0

    #The first time'1st text', The second time'Second text'Can be verified that is being passed and called as a parameter
    mailer_mock.assert_has_calls([call('1st text'), call('Second text')])

I want to control the return value

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # side_Pass a list of return values as an array to effect
    #Each time it is called, it will be returned in order from the beginning of the array
    #In this example, False is returned the first time and True is returned the second time.
    mailer_mock = mocker.patch.object(Mailer, 'send', side_effect = [False, True])

    messages = ['1st text', 'Second text']

    #Second Mailer.Since send returns True, you can verify the return value 1.
    assert hoge(messages) == 1

I want to raise an exception

test_hoge.py

from hoge import hoge
from mailer import Mailer
from unittest.mock import call

def test_hoge(mocker):
    # side_Specify an exception for effect
    #In this example, the first time is False and the second time is an exception.
    mailer_mock = mocker.patch.object(Mailer, 'send', side_effect = [False, Exception('error')])

    messages = ['1st text', 'Second text']

    #Second Mailer.Since send raises an exception, the return value 2 can be verified.
    assert hoge(messages) == 2