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Testing & modern typing

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

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How to Benchmark Python Code with pytest-benchmark and mocks

Use pytest-benchmark to measure function performance while combining Mock and patch for controlled test scenarios.

import time
from unittest.mock import Mock, patch

import pytest
from pytest_benchmark.fixture import BenchmarkFixture


def heavy_operation(data: list[int]) -> int:
    """Simulates a CPU-bound operation."""
    return sum(x * x for x in data)


def test_heavy_operation_benchmark(benchmark: BenchmarkFixture) -> None:…

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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 medium

How to Mock and Stub API Calls in Playwright E2E Tests with Python

This code demonstrates how to mock and stub API responses in Playwright end-to-end tests using Python's unittest.mock patch and Playwright's APIRequestContext.

playwright e2e-testing mocking

Python

import re
from unittest.mock import patch
from playwright.sync_api import sync_playwright

def verify_api_mock(page, mock_url, mock_response):
    with patch("playwright.sync_api.APIRequestContext.get") as mock_get:
        mock_get.return_value.json.return_value = mock_response
        mock_get.return_value.status_co…

13 0 Open

Testing & modern typing medium

How to Run an Integration Test with Docker Compose Mock in Python

Run a Python integration test against a docker-compose environment, using mocks to simulate service health and business logic responses.

docker integration-testing mocking

Python

import subprocess
import json
from typing import Dict

def run_integration_test() -> Dict[str, str]:
    """
    Simulates an integration test against a docker-compose environment
    using a mock service that returns canned responses.
    """
    # Mock docker-compose environment check
    env_ready = subprocess.run(…

15 0 Open

Testing & modern typing medium

How to Snapshot Test JSON with Mock in Python

Use pytest-snapshot to capture the exact output of a JSON-loading function, with and without mocking json.loads, so future changes are automatically detected.

pytest snapshot mock

Python

import json
from unittest.mock import Mock, patch
import pytest


def load_config(data):
    config = json.loads(data)
    return {"host": config["host"], "port": config["port"]}


def test_load_config_snapshot(snapshot):
    mock_data = json.dumps({"host": "localhost", "port": 8080, "extra": "ignored"})
    result = …

14 0 Open

Testing & modern typing medium

How to Use Mock Flip Mutation Testing in Python

Demonstrates how mutation testing tools flip Boolean literals (mock flip) in Python source to verify test suite effectiveness in catching logic changes.

mutation-testing testing bool

Python

import random

# In mutation testing, a "mock flip" intentionally changes a Boolean
# constant to False (or True) to see if the test suite catches it.
# This is a common "constant mutation" applied to a source file's literals.

def is_even(n: int) -> bool:
    """Return True if n is even. Contains a Boolean literal us…

13 0 Open

Testing & modern typing medium

How to Use Stubs, Fakes, Spies, and Mocks in Python Testing

Implement four types of test doubles — stubs, fakes, spies, and mocks — as subclasses of a PaymentGateway interface to replace real dependencies during testing.

testing mocks stubs

Python

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


class StubPaymentGateway(PaymentGateway):
    """Returns a fixed response without any logic."""
    def charge(self, amount):
        return {"success": True, "transaction_id": "stub-12345"}


class FakePaymentGateway(PaymentGatewa…

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Testing & modern typing medium

Use pytest fixture to mock a database connection in Python

This code shows how to use a pytest fixture and unittest.mock to replace a database connection with a Mock, enabling isolated tests without a real database.

pytest fixtures unittest.mock

Python

import pytest
import sqlite3
from unittest.mock import Mock

class Database:
    def __init__(self, connection):
        self.connection = connection

    def get_user(self, user_id):
        cursor = self.connection.cursor()
        cursor.execute("SELECT * FROM users WHERE id = ?", (user_id,))
        return cursor.…

19 0 Open

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