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How to Mock a Failing Dependency to Test Error Paths in Python
Inject a fake HTTP client that raises a connection error to test how code handles dependency failures without touching the network.
import requests
def fetch_user(user_id):
url = f"https://api.example.com/users/{user_id}"
response = requests.get(url, timeout=5)
response.raise_for_status()
return response.json()
def get_user_name(user_id, http_client):
try:
user_data = http_client(user_id)
return user_data["nam…How to Mock OpenAI Tool Call Messages in Python
Create an assistant message with a function tool call in OpenAI's chat format, useful for testing and mocking.
from openai import OpenAI
def mock_tool_call(tool_name: str, arguments: dict) -> dict:
"""Simulate a tool call message in OpenAI style."""
return {
"role": "assistant",
"content": None,
"tool_calls": [
{
"id": "call_" + "a1b2c3d4e5f6",
"type…How to Mock FFmpeg subprocess Calls in Python
Compress a video with ffmpeg while mocking subprocess.run to test the command construction without executing the actual encoder.
import subprocess
from unittest.mock import Mock, patch
def compress_video(input_path: str, output_path: str, crf: int = 23) -> None:
"""Compress a video using ffmpeg with a given CRF (quality) value."""
command = [
"ffmpeg",
"-i", input_path,
"-c:v", "libx264",
"-crf", str(cr…Map Partition Over Chunks in Python with Multiprocessing and Mock
Process data in chunks across multiple CPU cores using multiprocessing Pool.map, and mock the chunk function to test partitioning behavior without heavy computation.
from multiprocessing import Pool
from unittest.mock import patch, Mock
def process_chunk(chunk):
return [x * x for x in chunk]
def map_partition_over_chunks(data, chunk_size, process_func=process_chunk):
chunks = [data[i:i + chunk_size] for i in range(0, len(data), chunk_size)]
with Pool() as pool:
…How to Get Current Git Branch Name in Python with Mock Subprocess
Mocks the subprocess call to reliably test the current git branch name retrieval using GitPython.
import subprocess
from unittest.mock import patch, MagicMock
from git import Repo
import os
def get_current_branch(repo_path="."):
"""Get the current branch name of a git repository."""
repo = Repo(repo_path)
return repo.active_branch.name
if __name__ == "__main__":
# Mock subprocess to control the…How to Mock Git Pre-commit Hooks (black and ruff) in Python
Mock subprocess to test black and ruff pre-commit commands without actually running them, verifying exit codes.
import sys
import subprocess
from unittest.mock import patch
def run_hook(command: list[str]) -> int:
with patch("subprocess.run") as mock_run:
mock_run.return_value.returncode = 0
mock_run.return_value.stdout = f"Mocked: {' '.join(command)}"
result = subprocess.run(command, capture_output…How to Mock git sparse-checkout Paths in Python
Simulates git sparse-checkout configuration by writing desired paths to the sparse-checkout file without running git commands.
import subprocess
from pathlib import Path
import tempfile
def configure_sparse_checkout(repo_dir: Path, paths: list[str]) -> list[str]:
"""Simulate sparse checkout configuration by returning the paths that would be set."""
sparse_checkout_file = repo_dir / ".git" / "info" / "sparse-checkout"
sparse_chec…How to Mock open() in Python Using unittest.mock.patch
This code shows how to use unittest.mock.patch with mock_open to test a function that checks if a Git patch can be reverse-applied by reading file content.
import unittest
from unittest.mock import patch, mock_open
def apply_reverse_check(file_path, expected_patch):
"""
Check if a patch can be reverse-applied by comparing file content
with the expected patch's reverse result.
"""
try:
with open(file_path, "r") as f:
content = f.r…Mock smtplib to Test Patch Email Series in Python
Simulate sending a numbered series of patch emails with smtplib and verify the calls using unittest.mock without a real mail server.
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from unittest.mock import patch, Mock
def send_patch_series(subject_prefix, patches, smtp_host="localhost", smtp_port=25):
"""Simulate sending a series of patch emails."""
for i, patch_content in enumerate(patch…How to Create a Mock STS AssumeRole Credentials Dict in Python
Build a realistic AWS STS AssumeRole response dict with temporary credentials, expiry time, and assumed role ARN for local testing.
import json
from datetime import datetime, timedelta, timezone
def mock_sts_credentials(role_arn, session_name, duration=3600):
now = datetime.now(timezone.utc)
expiration = now + timedelta(seconds=duration)
credentials = {
"Credentials": {
"AccessKeyId": "ASIAEXAMPLEACCESSKEY",
…How to mock boto3 S3 upload in Python
Shows how to mock the boto3 S3 client with unit tests and wrap an upload function to return a dictionary with status details.
import boto3
from unittest.mock import Mock, patch
class S3Uploader:
def __init__(self, bucket_name):
self.bucket_name = bucket_name
self.s3 = boto3.client("s3", region_name="us-east-1")
def upload_file(self, local_path, s3_key):
self.s3.upload_file(local_path, self.bucket_name, s3_ke…Mock ECS Task Run Stop Status Dict in Python
Build a mock ECS task status dictionary with RUNNING/STOPPED states using the standard library.
from datetime import datetime, timezone
def mock_ecs_task_status(task_id: str, state: str = "RUNNING") -> dict:
"""Return a mock ECS task status dictionary."""
return {
"taskArn": f"arn:aws:ecs:us-east-1:123456789012:task/cluster/{task_id}",
"taskDefinition": "arn:aws:ecs:us-east-1:1234567890…How to Bind and Mock structlog Context in Python
Shows how to bind persistent key-value context to a structlog logger, unbind keys, and mock the logger in tests to verify context is passed correctly.
import structlog
from unittest.mock import patch
logger = structlog.get_logger()
def demo():
logger = structlog.get_logger()
logger = logger.bind(user_id=42, request_id="abc123")
logger.info("user logged in", action="login")
# Unbind a key
logger = logger.unbind("user_id")
logger.info("r…How to Mock BugSnag Notify in Python
Use unittest.mock to simulate BugSnag notifications, verify calls, and test error handling without external dependencies.
import mock
bugsnag = mock.MagicMock()
def notify_error(message, severity="error"):
bugsnag.notify(message, severity=severity)
if __name__ == "__main__":
notify_error("Test error", severity="warning")
bugsnag.notify.assert_called_once_with("Test error", severity="warning")
print("Mocked BugSnag noti…How to Mock Click CLI App Subcommands in Python
Simulate Click-style CLI subcommand calls in Python by using argparse with subparsers and mocking sys.argv in tests or scripts.
import sys
import argparse
def do_greet(args):
print(f"Hello, {args.name}!")
def do_goodbye(args):
print(f"Goodbye, {args.name}!")
def main():
parser = argparse.ArgumentParser(prog="clickapp")
subparsers = parser.add_subparsers(dest="command", required=True)
greet_parser = subparsers.add_par…How to Mock Fabric Connections in Python for Task Testing
Create a lightweight MockConnection class to replace fabric.Connection and test task functions without SSH.
from fabric import Connection
class MockConnection:
"""Minimal mock of fabric.Connection for task testing."""
def __init__(self):
self.commands = []
def run(self, command, **kwargs):
self.commands.append(command)
return f"OK: {command}"
def deploy(conn):
"""Deploy the app:…How to Mock a Fast uv pip sync in Python
Simulate a fast uv pip sync by mocking file operations and subprocess calls to test dependency installation workflows.
import os
import shutil
import subprocess
import sys
import tempfile
from pathlib import Path
def uv_pip_sync_fast_install_mock(requirements_text: str) -> dict:
"""Simulate a fast uv pip sync by mocking file operations and subprocess calls."""
mock_dir = Path(tempfile.mkdtemp(prefix="uv_mock_"))
req_lines…How to Mock a pipx Install Command in Python
Simulate a pipx install step by validating tool names and printing the exact command output a real pipx run would produce.
import subprocess
import sys
def install_with_pipx(tool_name: str) -> str:
"""
Mock a pipx install step by validating the tool name and
simulating the installation command output.
"""
allowed_tools = {"black", "flake8", "mypy", "ruff"}
if tool_name not in allowed_tools:
raise ValueErr…How to Type Check a Mock with pyright in Python
Shows how pyright validates a mock function against a TypedDict and Callable signature before runtime.
from typing import TypedDict, Callable
class User(TypedDict):
id: int
name: str
def get_user_name(user_id: int, get_user: Callable[[int], User]) -> str:
user = get_user(user_id)
return user["name"]
def mock_get_user(user_id: int) -> User:
return {"id": user_id, "name": f"User {user_id}"}
if…How to mock argparse nested subparsers in Python
Build an argparse parser with nested subparsers and test it using unittest.mock.patch for sys.argv and sys.stdout.
import argparse
from unittest.mock import patch
from io import StringIO
def build_parser():
parser = argparse.ArgumentParser(prog="app")
subparsers = parser.add_subparsers(dest="command", required=True)
# Outer subparser
outer = subparsers.add_parser("outer")
outer_sub = outer.add_subparsers(dest…Mocking loguru for Structured Logging in Python
Simulate loguru's structured logging with a custom mock that captures JSON-formatted log entries with bound context.
import json
import sys
from io import StringIO
from unittest.mock import patch
def mock_loguru():
# Simulate a structured logger with context binding
class StructuredLogger:
def __init__(self):
self.context = {}
def bind(self, **kwargs):
logger = StructuredLogger()
…How to Mock anyio.run Backends (asyncio vs trio) in Python
Demonstrates how to mock anyio.run to verify backend selection (asyncio or trio) without actually running the event loop.
import anyio
from unittest.mock import Mock, patch
async def fetch_data():
await anyio.sleep(0.1)
return {"data": 42}
def run_with_backend(backend: str):
async def main():
result = await fetch_data()
print(f"[{backend}] Result: {result}")
anyio.run(main, backend=backend)
if __nam…How to Mock asyncio.open_connection in Python
Mock asyncio.open_connection with AsyncMock to test async code without a real network connection.
import asyncio
from unittest.mock import AsyncMock, patch
async def fetch_data(reader: asyncio.StreamReader) -> str:
data = await reader.readline()
return data.decode().strip()
async def main() -> None:
# Mock asyncio.open_connection to simulate a server response
mock_reader = AsyncMock()
mock_…Mocking Trio's open_nursery and spawn with asyncio.TaskGroup
Show how to mock Trio's nursery pattern using Python's asyncio.TaskGroup to simulate task spawning and completion.
import asyncio
class MockSpawner:
async def spawn(self, nursery):
print("Spawning mock task...")
await asyncio.sleep(1)
print("Mock task completed")
async def open_nursery():
async with asyncio.TaskGroup() as nursery:
mock = MockSpawner()
nursery.create_task(mock.spawn…Browse by section
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