Reference library

Testing & modern typing

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

7 matches

Capture stdout and stderr with pytest capsys

Use pytest's capsys fixture to capture and assert on standard output and error streams in your tests.

import pytest

# Function under test
def greet(name):
    print(f"Hello, {name}!")
    print(f"Error: {name} not found", file=sys.stderr)

def test_captures_stdout_and_stderr(capsys):
    greet("Alice")
    captured = capsys.readouterr()
    
    assert "Hello, Alice!" in captured.out
    assert "Error: Alice not foun…

14 0 Open

Testing & modern typing easy

Generate Fake User Data with Faker in Python

Use the Faker library to generate realistic fake user profiles with names, emails, phone numbers, and addresses for tests or demos.

faker fake-data testing

Python

from faker import Faker

fake = Faker()

def generate_user():
    return {
        "name": fake.name(),
        "email": fake.email(),
        "phone": fake.phone_number(),
        "address": fake.address().replace("\n", ", "),
    }

if __name__ == "__main__":
    user = generate_user()
    for key, value in user.ite…

10 0 Open

Testing & modern typing easy

How to Capture Logging Records with pytest caplog in Python

Capture and assert on logging records in pytest using the built-in caplog fixture.

pytest logging testing

Python

import logging
import pytest

def divide(a, b):
    """Divide two numbers and log an error if b is zero."""
    if b == 0:
        logging.error("Division by zero attempted")
        return None
    logging.info(f"Dividing {a} by {b}")
    return a / b

def test_divide_logs_error(caplog):
    with caplog.at_level(logg…

15 0 Open

Testing & modern typing easy

How to Share Fixtures Across Tests with pytest conftest

Learn how to define pytest fixtures in conftest.py and control their scope (function, module, session) so every test in a directory reuses the same setup and teardown.

pytest fixtures conftest

Python

import pytest

@pytest.fixture
def sample_data():
    """Simple fixture available to all tests in this directory."""
    return {"name": "Alice", "age": 30}

@pytest.fixture(scope="session")
def session_data():
    """Fixture created once per test session."""
    return {"session_id": 12345}

@pytest.fixture(scope="mo…

13 0 Open

Testing & modern typing easy

How to Test Environment Variables with pytest monkeypatch in Python

Shows how to use pytest's monkeypatch fixture to set and delete environment variables for isolated tests.

pytest monkeypatch environment variables

Python

import os
import pytest

def get_database_url():
    return os.getenv("DATABASE_URL", "postgres://default")

def test_database_url_with_env(monkeypatch):
    monkeypatch.setenv("DATABASE_URL", "postgres://test-db")
    assert get_database_url() == "postgres://test-db"

def test_database_url_default(monkeypatch):
    m…

12 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 the pytest tmp_path Fixture for Temporary Directories

Use pytest's built-in tmp_path fixture to create a unique temporary directory per test for clean file I/O testing.

pytest tmp_path fixtures

Python

import pytest


def test_write_and_read_file(tmp_path):
    # tmp_path is a pytest fixture that provides a temporary directory
    # unique to each test invocation
    data_file = tmp_path / "data.txt"
    data_file.write_text("hello world")
    assert data_file.read_text() == "hello world"


def test_multiple_tmp_pat…

15 0 Open

Browse by section

Each section groups closely related Python snippets.