Template for using the built-in unit test module in Python3

test_foo.py

import unittest
from unittest.mock import MagicMock, patch


class TestFoo(unittest.TestCase):
    """blablabla

    To run all the tests in TestFoo, run command

        python3 -m unittest tests.test_foo.TestFoo

    To run individual test within TestFoo, add the method name to the command.

        python3 -m unittest tests.test_foo.TestFoo.test_some_method

    To run other test suites, change the class name.

        python3 -m unittest tests.test_foo.TestFooBar

    To run all the test suites in this file, use the following command.

        python3 -m unittest tests.test_foo
    """

    @classmethod
    def setUp(cls) -> None:
        """Set up stuff before each test.
        """
        pass

    @patch('some_module.other_module.some_variable', mock_variable)
    @patch('some_module.other_module.some_class')
    def test_es_state_with_pg_hash(self, mock_some_class):
        """This is an individual test.

        mock_some_class is a MagicMock of the original class `some_class`.
        `some_variable` has been replaced by `mock_variable`.

        NOTE: Read this article for how to use `patch` to patch classmethod/staticmethod and instance method:

        https://medium.com/python-pandemonium/python-mocking-you-are-a-tricksy-beast-6c4a1f8d19b2
        """
        instance_method_mock = mock_some_class.return_value.instance_method  # mock an instance method that requires instantiation of `some_class`
        class_or_static_method_mock = mock_some_class.class_or_static_method # mock a class or static method that does not require instantiation of `some_class`

        mock_some_class.run()

        for arg in instance_method_mock.call_args_list:
            self.assertTrue(arg == (1, 2, 3))  # examine the arguments passed to instance method each time it is called

While I still prefer pytest, if it takes a lot of effort to add a third party library in the tool chain just for unit test, the built-in unittest module is not that bad an alternative.