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Testing & modern typing

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

6 matches

Fix and Test a Regression Bug in Python with Unit Tests

This code implements a circle area function that raises ValueError for negative radii, then runs basic tests and a regression check for that edge case.

regression-testing unit-testing math

Python

import math

def calculate_area(radius):
    """Calculate the area of a circle given its radius."""
    if radius < 0:
        raise ValueError("Radius cannot be negative")
    return math.pi * radius ** 2

def main():
    test_cases = [0, 1, 2.5, 5, 10]
    
    print("Circle Area Calculator")
    print("-" * 30)
   …

16 0 Open

Testing & modern typing medium

How to Mock a Factory Boy Model Instance in Python

Create a factory boy factory, then patch its Meta.model with a Mock to control instance behavior in tests.

factory-boy mocking unit-testing

Python

import factory
from dataclasses import dataclass
from unittest.mock import Mock, patch
import builtins


@dataclass
class User:
    name: str
    age: int


class UserFactory(factory.Factory):
    class Meta:
        model = User

    name = "Alice"
    age = 30


def get_user_name(user):
    return user.name


def ma…

15 0 Open

Testing & modern typing medium

How to Mock an Object Method in Python unittest

Mock a method on an instance or class with @patch.object, set its return value, and assert its call arguments in Python unittest.

unittest mock patch

Python

import unittest
from unittest.mock import patch

class Calculator:
    def add(self, a, b):
        return a + b
    
    def multiply(self, a, b):
        return a * b

class TestCalculator(unittest.TestCase):
    def test_add_normal(self):
        calc = Calculator()
        result = calc.add(2, 3)
        self.asse…

14 0 Open

Testing & modern typing easy

How to Mock pathlib Path.read_text with mock_open in Python

Mock pathlib.Path.read_text using patch and mock_open to test file-reading code without touching the filesystem.

testing mock pathlib

Python

import pathlib
from unittest.mock import mock_open, patch

def read_config(filepath: pathlib.Path) -> str:
    """Read file content with pathlib."""
    return filepath.read_text()

if __name__ == "__main__":
    mock_data = "version: 1.0\nname: demo-app"
    
    with patch("pathlib.Path.open", mock_open(read_data=mo…

14 0 Open

Testing & modern typing easy

How to Mock requests.get in Python

Mock requests.get with unittest.mock to test code that makes HTTP calls without hitting the network.

mocking requests unit-testing

Python

import requests
from unittest.mock import Mock, patch

def fetch_user_data(user_id):
    response = requests.get(f"https://api.example.com/users/{user_id}")
    return response.json()

def process_user(user_id):
    mock_response = Mock()
    mock_response.json.return_value = {"id": user_id, "name": "Alice", "age": 30…

12 0 Open

Testing & modern typing easy

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

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