Reference library

Testing & modern typing

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

5 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)
   …

18 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

Testing & modern typing easy

How to Use setUp and tearDown in Python unittest TestCase

Demonstrates how to structure unit tests with setUp and tearDown methods in Python's unittest framework for reusable test fixtures.

unittest testing setupteardown

Python

import unittest


class ExampleTest(unittest.TestCase):
    def setUp(self):
        self.data = [1, 2, 3]

    def tearDown(self):
        self.data = None

    def test_length(self):
        self.assertEqual(len(self.data), 3)

    def test_contains(self):
        self.assertIn(2, self.data)


if __name__ == "__main…

13 0 Open

Testing & modern typing easy

How to use Optional type hint in Python

Use the Optional type hint to indicate a parameter can be a string or None, with an example function that handles both cases.

typing optional type-hints

Python

from typing import Optional

def greet(name: Optional[str]) -> str:
    if name is None:
        return "Hello, anonymous!"
    else:
        return f"Hello, {name}!"

if __name__ == "__main__":
    print(greet("Alice"))
    print(greet(None))

11 0 Open

Testing & modern typing easy

Table-Driven Tests in Python (unittest)

Run a single unittest test against many input cases using a list of tuples and subTest.

unittest table-driven testing

Python

import unittest

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

class TestAddFunction(unittest.TestCase):

    def test_add_with_table(self):
        cases = [
            (1, 2, 3),
            (-1, 1, 0),
            (0, 0, 0),
            (2, -3, -1),
        ]
        for x, y, expected in cases:
            with self.subTest(x…

15 0 Open

Browse by section

Each section groups closely related Python snippets.