3.1. Unit Testing


Figure 3.21. Development driven tests

3.1.1. Glossary


A method stub or simply stub in software development is a piece of code used to stand in for some other programming functionality. A stub may simulate the behavior of existing code (such as a procedure on a remote machine) or be a temporary substitute for yet-to-be-developed code. Stubs are therefore most useful in porting, distributed computing as well as general software development and testing.


In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways. In a unit test, mock objects can simulate the behavior of complex, real objects and are therefore useful when a real object is impractical or impossible to incorporate into a unit test.


In computer programming, unit testing is a software testing method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures, are tested to determine whether they are fit for use.

3.1.2. Running tests

3.1.3. Running tests with your IDE

  • View menu -> Run... -> Unittest in myfunction

3.1.4. From code

if __name__ == "__main__":
    import unittest

3.1.5. From command line

Display only errors. With -v display progress:

$ python -m unittest myfile.py
$ python -m unittest -v myfile.py

3.1.6. Example 1

Code 3.65. Example unittest code coverage

from dataclasses import dataclass
from datetime import datetime, timezone
from unittest import TestCase

class User:
    firstname: str
    lastname: str
    date_of_birth: datetime | None = None
    permission: list = ()

    def __post_init__(self):
        self.permission = list(self.permission)

        if self.date_of_birth and self.date_of_birth.tzinfo != timezone.utc:
            raise ValueError

    def add_permission(self, permission):

    def remove_permission(self, permission):

    def __str__(self):
        return f'User(firstname="{self.firstname}", lastname="{self.lastname}")'

class UserTest(TestCase):

    def setUpClass(cls) -> None:

    def tearDownClass(cls) -> None:

    def setUp(self) -> None:
        now = datetime.now(tz=timezone.utc)
        self.user = User(firstname='Jan', lastname='Twardowski', date_of_birth=now)

    def tearDown(self) -> None:

    def test_create_user(self):
        user = User(firstname='Jan', lastname='Twardowski')
        self.assertEqual(user.firstname, 'Jan')
        self.assertEqual(user.lastname, 'Twardowski')

    def test_permission_add(self):
        self.assertIn('read', self.user.permission)

    def test_permission_remove(self):
        self.assertNotIn('read', self.user.permission)

    def test_date_of_birth_in_utc(self):
        self.assertEqual(self.user.date_of_birth.tzinfo, timezone.utc)

    def test_date_of_birth_not_in_utc(self):
        with self.assertRaises(ValueError):
            now = datetime.now()
            user = User(firstname='Jan', lastname='Twardowski', date_of_birth=now)
            self.assertEqual(user.date_of_birth.tzinfo, timezone.utc)

    def test_str(self):
        self.assertEqual(str(self.user), 'User(firstname="Jan", lastname="Twardowski")')

3.1.7. Example 2

Code 3.66. Example unittest code coverage
from unittest import TestCase

class Temperature:
    def __init__(self, kelvin=None, celsius=None, fahrenheit=None):
        values = [x for x in [kelvin, celsius, fahrenheit] if x]

        if len(values) < 1:
            raise ValueError('Need argument')

        if len(values) > 1:
            raise ValueError('Only one argument')

        if celsius is not None:
            self.kelvin = celsius + 273.15
        elif fahrenheit is not None:
            self.kelvin = (fahrenheit - 32) * 5 / 9 + 273.15
            self.kelvin = kelvin

        if self.kelvin < 0:
            raise ValueError('Temperature in Kelvin cannot be negative')

    def __str__(self):
        return f'Temperature = {self.kelvin} Kelvins'

class TemperatureTest(TestCase):
    def test_creating_temperature(self):
        with self.assertRaises(ValueError):

    def test_setting_temperature(self):
        temp = Temperature(10)
        self.assertEqual(temp.kelvin, 10)

    def test_temp_from_celsius(self):
        temp = Temperature(celsius=1)
        self.assertEqual(temp.kelvin, 274.15)

    def test_temp_from_fahrenheit(self):
        temp = Temperature(fahrenheit=1)
        self.assertAlmostEqual(temp.kelvin, 255.928, places=3)

    def test_invalid_initialization(self):
        with self.assertRaises(ValueError):
            Temperature(celsius=1, kelvin=1)

    def test_negative_kelvins(self):
        with self.assertRaises(ValueError):

        with self.assertRaises(ValueError):

        with self.assertRaises(ValueError):

    def test_to_string(self):
        temp = Temperature(kelvin=10)
        self.assertEqual(str(temp), 'Temperature = 10 Kelvins')

        temp = Temperature(celsius=10)
        self.assertEqual(str(temp), 'Temperature = 283.15 Kelvins')

3.1.8. Example 3

Code 3.67. Example unittest code coverage
from dataclasses import dataclass
from unittest import TestCase

class Longitude:
    value: float

    def __post_init__(self):
        if self.value > 180:
            raise ValueError
        if self.value < -180:
            raise ValueError

class Latitude:
    value: float

    def __post_init__(self):
        if self.value > 90:
            raise ValueError
        if self.value < -90:
            raise ValueError

class GEOCoordinates:
    lat: Latitude
    lon: Longitude

class LongitudeTest(TestCase):
    def test_init_latitude(self):
        l = Latitude(0)
        self.assertEqual(l.value, 0)

    def test_invalid(self):
        with self.assertRaises(ValueError):

        with self.assertRaises(ValueError):

class LatitudeTest(TestCase):
    def test_init_latitude(self):
        l = Latitude(0)
        self.assertEqual(l.value, 0)

    def test_invalid(self):
        with self.assertRaises(ValueError):

        with self.assertRaises(ValueError):

class GEOCoordinatesTest(TestCase):
    def test_set_longitude(self):
        lat = Latitude(-90)
        lon = Longitude(20)
        geo = GEOCoordinates(lat, lon)

3.1.9. Example 4

Code 3.68. Example unittest code coverage
from dataclasses import dataclass
from datetime import date, datetime, timezone
from unittest import TestCase

class Astronaut:
    name: str
    agency: str = 'NASA'
    date_of_birth: date | None = None
    first_step: datetime | None = None

    def __str__(self):
        return f'My name... {self.name}'

    def __post_init__(self):
        if self.first_step and self.first_step.tzinfo != timezone.utc:
            raise ValueError('Timezone must by UTC')

class AstronautTest(TestCase):
    def setUp(self):
        self.astro = Astronaut(name='José Jiménez', agency='NASA')

    def test_recruiting_new_astronaut(self):
        jose = Astronaut(name='José Jiménez')
        self.assertEqual(jose.name, 'José Jiménez')

    def test_default_agency(self):
        jose = Astronaut(name='José Jiménez')
        self.assertEqual(jose.agency, 'NASA')

    def test_date_of_birth(self):
        jose = Astronaut(name='José Jiménez', date_of_birth=date(1961, 4, 12))
        self.assertEqual(jose.date_of_birth, date(1961, 4, 12))

    def test_first_step_in_utc(self):
        step = datetime(1969, 7, 21, 14, tzinfo=timezone.utc)
        jose = Astronaut(name='José Jiménez', first_step=step)
        self.assertEqual(jose.first_step.tzinfo, timezone.utc)

    def test_first_step_not_in_utc(self):
        step = datetime(1969, 7, 21, 14)

        with self.assertRaises(ValueError):
            Astronaut(name='José Jiménez', first_step=step)

    def test_hello(self):
        self.assertEqual(str(self.astro), 'My name... José Jiménez')

3.1.10. Example 5

Code 3.69. Example unittest code coverage
import unittest

class Rectangle:
    def __init__(self, bok_a: float | int, bok_b: float | int) -> None:
        if not isinstance(bok_a, float|int) or bok_a <= 0:
            raise ValueError('Side A cannot be negative')

        if not isinstance(bok_b, float|int) or bok_b <= 0:
            raise ValueError('Side B cannot be negative')

        self.side_a = float(bok_a)
        self.side_b = float(bok_b)

    def area(self) -> float:
        return self.side_a * self.side_b

    def circumference(self) -> float:
        return 2 * (self.side_a + self.side_b)

    def __str__(self) -> str:
        return f'Rectangle(a={self.side_a}, b={self.side_b})'

class RectangleTest(unittest.TestCase):

    def setUp(self):
        self.rectangle = Rectangle(bok_a=10, bok_b=20)

    def test_create_rectangle(self):
        Rectangle(bok_a=5, bok_b=10)

    def test_create_rectangle_with_invalid_side(self):
        with self.assertRaises(ValueError):
            Rectangle(bok_a='a', bok_b=20)

        with self.assertRaises(ValueError):
            Rectangle(bok_a=20, bok_b='b')

        with self.assertRaises(ValueError):
            Rectangle(bok_a='b', bok_b='b')

    def test_create_rectangle_side_zero(self):
        with self.assertRaises(ValueError):
            Rectangle(bok_a=0, bok_b=20)

        with self.assertRaises(ValueError):
            Rectangle(bok_a=20, bok_b=0)

        with self.assertRaises(ValueError):
            Rectangle(bok_a=0, bok_b=0)

    def test_create_rectangle_side_negative(self):
        with self.assertRaises(ValueError):
            Rectangle(bok_a=-3, bok_b=20)

        with self.assertRaises(ValueError):
            Rectangle(bok_a=20, bok_b=-3)

        with self.assertRaises(ValueError):
            Rectangle(bok_a=-1, bok_b=-3)

    def test_create_rectangle_with_one_side(self):
        with self.assertRaises(TypeError):

        with self.assertRaises(TypeError):

    def test_create_rectangle_and_store_values(self):
        p = Rectangle(bok_a=5, bok_b=10)
        self.assertEqual(p.side_a, 5)
        self.assertEqual(p.side_b, 10)

    def test_create_rectangle_valid(self):
        self.assertEqual(self.rectangle.side_a, 10)
        self.assertEqual(self.rectangle.side_b, 20)

    def test_area(self):
        self.assertEqual(self.rectangle.area(), 200.0)

    def test_circumference(self):
        self.assertEqual(self.rectangle.circumference(), 60)

    def test_stringify_rectangle(self):
        self.assertEqual(str(self.rectangle), 'Rectangle(a=10.0, b=20.0)')

if __name__ == '__main__':

3.1.11. Mock

  • Mock and MagicMock objects create all attributes and methods as you access them and store details of how they have been used.

from unittest.mock import MagicMock

thing = ProductionClass()
thing.method = MagicMock(return_value=3)

thing.method(3, 4, 5, key='value')
# 3

thing.method.assert_called_with(3, 4, 5, key='value')

3.1.12. Side effect

  • Raising an exception when a mock is called

from unittest.mock import Mock

mock = Mock(side_effect=KeyError('foo'))

# Traceback (most recent call last):
# KeyError: 'foo'

3.1.13. patch

  • The object you specify will be replaced with a mock (or other object) during the test and restored when the test ends

from unittest.mock import patch

def test(MockClass1, MockClass2):
    assert MockClass1 is module.ClassName1
    assert MockClass2 is module.ClassName2
    assert MockClass1.called
    assert MockClass2.called

from unittest.mock import patch

class MyClass:
    def method(self)

with patch.object(MyClass, 'method', return_value=None) as mock_method:
    thing = MyClass()
    thing.method(1, 2, 3)

mock_method.assert_called_once_with(1, 2, 3)

3.1.14. Stub

  • writing classes or functions but not yet implementing them

  • After you have planned a module or class, for example by drawing it's UML diagram, you begin implementing it.

  • As you may have to implement a lot of methods and classes, you begin with stubs.

  • This simply means that you only write the definition of a function down and leave the actual code for later.

class Foo:
     def bar(self):
         raise NotImplementedError

     def tank(self):
         raise NotImplementedError

3.1.15. Assignments

Code 3.70. Solution
* Assignment: DevOps Unittest Rectangle
* Complexity: medium
* Lines of code: 100 lines
* Time: 21 min

    1. Write unittest for `Rectangle`
    2. Run doctests - all must succeed

    1. Napisz testy jednostkowe dla `Rectangle`
    2. Uruchom doctesty - wszystkie muszą się powieść

import unittest

class Rectangle:

    def __init__(self, a, b):
        self.side_a = a
        self.side_b = b

        if a <= 0 or b <= 0:
            raise ValueError('Side length must be positive')

    def area(self) -> int:
        return self.side_a * self.side_b

    def circumference(self) -> int:
        return (self.side_a + self.side_b) * 2

    def __str__(self):
        return f'Rectangle({self.a}, {self.b})'

Code 3.71. Solution
* Assignment: DevOps Unittest Dragon
* Complexity: medium
* Lines of code: 100 lines
* Time: 21 min

    1. Write unittest for the dragon from :ref:`Dragon Alpha`
    2. Run doctests - all must succeed

    1. Napisz testy jednostkowe dla Smoka z :ref:`Dragon Alpha`
    2. Uruchom doctesty - wszystkie muszą się powieść

from random import randint
from unittest import TestCase

class Config:

class Status:
    ALIVE = 'alive'
    DEAD = 'dead'

class Dragon:
    DAMAGE_MIN = 5
    DAMAGE_MAX = 20

    class IsDead(Exception):

    def __init__(self, name, x=0, y=0):
        self.status = Status.ALIVE
        self.name = name
        self.position_x = x
        self.position_y = y

    def get_position(self):
        return self.position_x, self.position_y

    def set_position(self, x, y):
        if x > Config.RESOLUTION_X_MAX:
            x = Config.RESOLUTION_X_MAX

        if x < Config.RESOLUTION_X_MIN:
            x = Config.RESOLUTION_X_MIN

        if y > Config.RESOLUTION_Y_MAX:
            y = Config.RESOLUTION_Y_MAX

        if y < Config.RESOLUTION_Y_MIN:
            y = Config.RESOLUTION_Y_MIN

        self.position_x = x
        self.position_y = y

    def move(self, down=0, left=0, up=0, right=0):
        x, y = self.get_position()
        x += right - left
        y += down - up
        self.set_position(x, y)

    def make_damage(self):
        if self.is_dead():
            raise Dragon.IsDead
        return randint(self.DAMAGE_MIN, self.DAMAGE_MAX)

    def is_dead(self):
        if self.status == Status.DEAD:
            return True
            return False