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Testing & modern typing

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

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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…

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Testing & modern typing easy

How to Mock return_value with MagicMock in Python unittest

Use unittest.mock.MagicMock to replace a dependency and set return_value to control what a mocked method returns during unit tests.

unittest mock magicmock

Python

import unittest
from unittest.mock import MagicMock


class PaymentGateway:
    def charge(self, amount):
        raise NotImplementedError


class OrderService:
    def __init__(self, gateway):
        self.gateway = gateway

    def process_order(self, amount):
        return self.gateway.charge(amount)


class Test…

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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…

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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…

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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…

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