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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…

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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…

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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…

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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…

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Testing & modern typing easy

How to Mock subprocess.run returncode in Python

Simulate subprocess.run return codes in tests with unittest.mock.patch and CompletedProcess.

unittest mock subprocess

Python

import subprocess
from unittest.mock import patch


def run_command(cmd):
    result = subprocess.run(cmd, capture_output=True, text=True)
    return result.returncode


if __name__ == "__main__":
    with patch("subprocess.run") as mock_run:
        # Simulate a successful command (returncode 0)
        mock_run.retu…

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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

Mock datetime.now to freeze time in Python

Use unittest.mock.patch to replace datetime.now with a fixed value so your code always sees the same time during tests.

datetime mock unittest

Python

from datetime import datetime
from unittest.mock import patch

def current_message():
    now = datetime.now()
    return f"Current time: {now:%Y-%m-%d %H:%M:%S}"

if __name__ == "__main__":
    with patch("__main__.datetime") as mock_dt:
        mock_dt.now.return_value = datetime(2024, 3, 15, 10, 30, 0)
        prin…

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