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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

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How to Parametrize pytest Tests with Multiple Input Cases in Python

This code shows how to use pytest's @pytest.mark.parametrize decorator to run the same test function across multiple input-output combinations, checking that an add function behaves correctly for each case.

pytest parametrize testing

Python

import pytest

def add(a, b):
    return a + b


@pytest.mark.parametrize("a,b,expected", [
    (1, 2, 3),
    (5, 5, 10),
    (-1, 1, 0),
    (0, 0, 0),
    (10, -3, 7),
])
def test_add(a, b, expected):
    assert add(a, b) == expected


if __name__ == "__main__":
    pytest.main([__file__, "-v"])

14 0 Open

Testing & modern typing easy

How to Skip Slow Tests with pytest.mark in Python

Use pytest.mark.skip and custom marks like @pytest.mark.slow to skip or deselect slow tests during test runs.

pytest testing skip

Python

import pytest
import time


def test_fast():
    assert 1 + 1 == 2


@pytest.mark.skip(reason="slow test skipped by default")
def test_slow():
    time.sleep(5)
    assert True


@pytest.mark.slow
def test_marked_slow():
    time.sleep(5)
    assert True


if __name__ == "__main__":
    pytest.main([__file__, "-v", "-…

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Testing & modern typing easy

How to Use Union Type Hints in Python

This code demonstrates how to use Union type hints to specify that a parameter can accept multiple types (int, float, str) and handle them accordingly.

type-hints union typing

Python

from typing import Union

def process_value(value: Union[int, float, str]) -> str:
    if isinstance(value, (int, float)):
        return f"Number: {value * 2}"
    return f"String: {value.upper()}"

if __name__ == "__main__":
    print(process_value(10))
    print(process_value(3.14))
    print(process_value("hello"))

14 0 Open

Testing & modern typing easy

Mock datetime with time-machine in Python

Use the time-machine library to travel to a fixed datetime when running tests or scripts, mocking datetime.utcnow().

testing datetime mock

Python

from time_machine import travel
from datetime import datetime


@travel("2020-01-01 10:30:00")
def check_date():
    return datetime.utcnow()


if __name__ == "__main__":
    print(check_date())

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