Python Unittest Cheet Sheet#

# Makefile
# https://github.com/databrickslabs/dbx/blob/main/Makefile

SHELL=/bin/bash
VENV_NAME := $(shell [ -d venv ] && echo venv || echo .venv)
PYTHON=${VENV_NAME}/bin/python
FOLDER_FOR_COV=module1_folder module2_folder
COVERAGE_THRESHOLD=80

test:
    $(PYTHON) -m pytest tests/unit/ -v -s -n auto --cov ${FOLDER_FOR_COV} \
        --cov-report=html \
        --cov-report=term-missing:skip-covered \
        --cov-fail-under=$(COVERAGE_THERSHOLD)

$ pytest --help | grep -i ipython
                        --pdbcls=IPython.terminal.debugger:TerminalPdb

[pytest]
addopts = --pdbcls=IPython.terminal.debugger:TerminalPdb

[tool.pytest.ini_options]
testpaths = ["tests/unit"]
addopts = """
    -v -s
    --junitxml=junit/test-results.xml
    --cov <app_folder_name>
    --cov-report=html
    --cov-report=xml
    --cov-report=term-missing:skip-covered
    --cov-fail-under=0
    --pdbcls=IPython.terminal.debugger:TerminalPdb
    """

# when pytest --pdb is stopping at a failure
>>> import sys

>>> sys.last_traceback.tb_lineno
1641

>>> sys.last_traceback.tb_frame
<frame at 0x7fcca5f89a00, file '/home/xiang/git/myPython/venv/lib/python3.8/site-packages/_pytest/python.py', line 1641, code runtest>

>>> sys.last_value
AssertionError('assert result == "ok"',)

>>> sys.last_type
<class 'AssertionError'>

<!-- more -->

pytest -k "send_http" -v
pytest -k "not send_http" -v
pytest -k "send_http or quick" -v

@pytest.mark.xfail(strict=True, reason="")
def test_function():
    ...

<!-- more -->

@pytest.mark.parametrize(
    "a, b, expected",
    [
        (1, 2, 3),
        (3, 3, 6),
    ],
)
def test_sum(a, b, expected):
    total = a + b
    assert total == expected

# content of test_indirect_list.py

import pytest


@pytest.fixture(scope="function")
def x(request):
    return request.param * 3


@pytest.fixture(scope="function")
def y(request):
    return request.param * 2


@pytest.mark.parametrize("x, y", [("a", "b")], indirect=["x"])
def test_indirect(x, y):
    assert x == "aaa"
    assert y == "b"

>>> vals = {(1, 2): 1, (2, 3): 2}
>>> def side_effect(*args):
...    return vals[args]
...
>>> mock = MagicMock(side_effect=side_effect)
>>> mock(1, 2)
1
>>> mock(2, 3)
2

>>> mock = MagicMock(side_effect=[4, 5, 6])
>>> mock()
4
>>> mock()
5
>>> mock()
6

from dataclasses import dataclass
from unittest.mock import Mock


@dataclass
class A:
    name: str


@dataclass
class B:
    name: str


@dataclass
class InventoryItem:
    a: A
    b: B


def test_class_inventory_item():
    mock_inventory_item = InventoryItem(*[Mock() for _ in range(2)])

    # or using inspect to get dynamically the class parameters count
    from inspect import signature
    mock_inventory_item = InventoryItem(*[Mock() for _ in range(len(signature(InventoryItem).parameters))])

# replace function bar of module x by another function fake_bar with unittest.mock.patch
# we can assert the mocked function with mock_bar
from unittest.mock import patch

def foo(arg1, arg2):
    r = bar(arg1)

def test_foo():
   with patch("x.bar", wraps=fake_bar) as mock_bar:
      actual = foo(arg1, arg2)
      assert actual == expected
      mock_bar.assert_called_once_with(arg1)

# replace function bar of module x by another function fake_bar with monkeypatch
# we cannot assert the mocked function, but we don't need to give the x module in full string format.

def foo(arg1, arg2):
    r = bar(arg1)

def test_foo(monkeypatch):
    monkeypatch.setattr(x, "bar", fake_bar)

# replace function bar of module x by another function fake_bar with pytest-mock
# we assert the mocked function

def foo(arg1, arg2):
    r = bar(arg1)

def test_foo(monkeypatch):
    mock_bar = mocker.patch("x.bar", wraps=fake_bar)

monkeypatch.setattr(obj, name, value, raising=True)
monkeypatch.delattr(obj, name, raising=True)

# contents of our test file e.g. test_code.py
import pytest


@pytest.fixture
def mock_env_user(monkeypatch):
    monkeypatch.setenv("USER", "TestingUser")


@pytest.fixture
def mock_env_missing(monkeypatch):
    monkeypatch.delenv("USER", raising=False)


# notice the tests reference the fixtures for mocks
def test_upper_to_lower(mock_env_user):
    assert get_os_user_lower() == "testinguser"


def test_raise_exception(mock_env_missing):
    with pytest.raises(OSError):
        _ = get_os_user_lower()

# file a.py
TEST_USER = os.getenv("TEST_USER")

def get_test_user():
    return(TEST_USER)


# file test_a.py
import pytest

from a import get_test_user

@pytest.fixture
def mock_env_user(monkeypatch):
    monkeypatch.setenv("TEST_USER", "TestingUser")

def test_get_test_user(mock_env_user):
    assert get_test_user() == "testinguser"

# file a.py

def get_test_user():
    TEST_USER = os.getenv("TEST_USER")
    return(TEST_USER)

# patch one key at each patch
monkeypatch.setitem(app.DEFAULT_CONFIG, "user", "test_user")
monkeypatch.setitem(app.DEFAULT_CONFIG, "database", "test_db")
monkeypatch.delitem(app.DEFAULT_CONFIG, "name", raising=False)

monkeypatch.syspath_prepend(path)

monkeypatch.chdir(path)

# run on 4 CPUs
pytest -n 4

# run on a number of CPUs calculated automatically by the python built-in multiprocessing module
pytest -n auto

# run on a number of CPUs calculated automatically by the module psutil, you need such module if you have logical cpus as well as certain imposed limitations (like container runtimes with cpu limits)
# ref. https://stackoverflow.com/a/14840102/5095636
# ref. https://docs.python.org/3/library/multiprocessing.html#multiprocessing.cpu_count
pip install pytest-xdist[psutil]
pytest -n auto

>>> mock = Mock(name='Thing', return_value=None)
>>> mock(1, 2, 3)
>>> mock.asssert_called_once_with(4, 5, 6)
<Mock name='Thing.asssert_called_once_with()' id='140160334650144'>

>>> from urllib import request
>>> mock = Mock()
>>> mock.asssert_called_with()
<Mock name='mock.asssert_called_with()' id='140160336271776'>

# using simple speccing, mock.asssert_called_with() is detected as an error
>>> mock = Mock(spec=request.Request)
>>> mock.asssert_called_with()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: Mock object has no attribute 'asssert_called_with'

# still using simple speccing, mock.data.asssert_called_with() is detected as an mocked method, no errors.
# so simple speccing doesnt' work for nested objects
>>> mock.data.asssert_called_with()
<Mock name='mock.data.asssert_called_with()' id='140160336027120'>

>>> from urllib import request
>>> patcher = patch('__main__.request', autospec=True)
>>> mock_request = patcher.start()

>>> request is mock_request
True

# mock_request.Request has the spec='Request' now
>>> mock_request.Request
<MagicMock name='request.Request' spec='Request' id='...'>

# the real request object doesn't have the static data attribute, so autospecced object doesn't have it neither.
>>> mock_request.data
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/unittest/mock.py", line 637, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'data'

>>> from urllib import request
>>> mock_request = create_autospec(request)
>>> mock_request.Request('foo', 'bar')
<NonCallableMagicMock name='mock.Request()' spec='Request' id='...'>

>>> from unittest.mock import Mock
>>> mock = Mock(return_value=None)
>>> mock('foo', bar=object())
>>> mock.assert_called_once_with('foo', bar=ANY)

>>> from unittest.mock import Mock, call
>>> m = Mock(return_value=None)
>>> m(1)
>>> m(1, 2)
>>> m(object())
>>> m.mock_calls == [call(1), call(1, 2), ANY]