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How to Mock subprocess Calls in Python with unittest.mock
A Python script that wraps Vagrant up/destroy commands using subprocess, with tests that mock the subprocess call to simulate outputs and errors.
import subprocess
from unittest.mock import patch, Mock
def run_vagrant(action: str) -> str:
result = subprocess.run(
["vagrant", action],
capture_output=True,
text=True,
check=False,
)
return result.stdout.strip()
def vagrant_wrapper(action: str) -> str:
if action n…Mock a Helm Upgrade Install Command in Python
Use unittest mock to simulate a Helm upgrade --install call for testing automation scripts without a real cluster.
from unittest.mock import MagicMock, patch
class HelmClient:
def upgrade_install(self, release, chart, namespace="default"):
# Simulates the helm upgrade --install command
return f"Release {release} upgraded/installed in {namespace} using chart {chart}"
@patch("helm_client.HelmClient.upgrade_in…How to Mock Git Cherry-Pick in Python for Tests
Mock the `repo.git.cherry_pick` method with `unittest.mock` to test a Git cherry-pick helper without a real repository.
from unittest.mock import patch, MagicMock
class GitCherryPicker:
def __init__(self):
self.applied_commits = []
def cherry_pick(self, commit_hash, repo):
try:
result = repo.git.cherry_pick(commit_hash)
self.applied_commits.append(commit_hash)
return f"A…How to Mock Git Stash and Pop in Python
Mock Git stash, apply, and pop operations using unittest.mock so you can test Git automation without touching a real repository.
import git
from unittest.mock import Mock, patch
def stash_and_pop(repo):
"""Mock a stash operation and then pop it back."""
repo.git.stash("save", "WIP: temp changes")
stashed_output = repo.git.stash("list")
# Simulate the stash was applied, then pop
repo.git.stash("apply", "stash@{0}")
…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…How to Mock subprocess.run in Python Tests
Mock subprocess.run to test a Git submodule update command without executing it in your test suite.
import subprocess
from unittest.mock import Mock, patch
def update_submodules():
subprocess.run(["git", "submodule", "update", "--init", "--recursive"], check=True)
with patch("subprocess.run") as mock_run:
mock_run.return_value = Mock(returncode=0)
update_submodules()
mock_run.assert_called_once_wit…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 Mock Azure Key Vault Secret Get in Python
Mock an Azure Key Vault client's get_secret method with unittest.mock to test functions that retrieve secret values without hitting the real service.
import unittest
from unittest.mock import MagicMock, patch
def get_secret(key_vault_client, secret_name):
"""Retrieve a secret value from an Azure Key Vault client."""
secret = key_vault_client.get_secret(secret_name)
return secret.value
class TestKeyVaultSecretGet(unittest.TestCase):
def test_get_…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…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 CLI Output in Typer with unittest.mock
Mock and capture Typer CLI output using unittest.mock.patch and io.StringIO for testing command-line applications.
import typer
from unittest.mock import patch
import io
app = typer.Typer()
@app.command()
def greet(name: str, age: int = 18, uppercase: bool = False):
"""Greet a person with optional formatting."""
message = f"Hello {name}, age {age}"
if uppercase:
message = message.upper()
typer.echo(messag…How to Mock a PEP 517 Build Backend in Python
Use unittest.mock.Mock to simulate a PEP 517 backend interface, stub build hooks, and verify calls for package build automation.
import json
from unittest.mock import Mock
# Simulate a PEP 517 backend interface
class Pep517Backend:
def build_wheel(self, wheel_directory, config_settings=None, metadata_directory=None):
return f"{wheel_directory}/mock_package-1.0.0-py3-none-any.whl"
def get_requires_for_build_wheel(self, config_s…How to Mock isort Output to Test Import Sorting in Python
Uses isort with check mode and a unittest mock to verify whether a Python source string has correctly sorted imports.
import isort
from unittest.mock import patch
code = """
import os
import sys
import json
import pathlib
"""
def check_imports_sorted(code_str):
with patch("isort.api.output") as mock_output:
isort.code(code_str, check=True, show_diff=True)
return mock_output.called
if __name__ == "__main__":
…How to Mock setuptools_scm get_version in Python
This code demonstrates how to mock setuptools_scm.get_version in Python using unittest.mock.patch to test version retrieval logic without installing or relying on the actual package.
```python
from unittest.mock import patch
def get_version_from_scm():
try:
import setuptools_scm
return setuptools_scm.get_version()
except (ImportError, LookupError):
return None
if __name__ == "__main__":
with patch("setuptools_scm.get_version", return_value="1.2.3"):
pr…How to Mock subprocess.run for Black Formatter in Python
Use unittest.mock to simulate subprocess.run calls in a Python function that runs the Black formatter, allowing isolated testing without executing external commands.
import subprocess
from unittest.mock import Mock, patch
def run_black_formatter(file_path: str, check_only: bool = False) -> dict:
"""Run black formatter on a file via subprocess."""
cmd = ["black", "--check" if check_only else "-", file_path]
result = subprocess.run(cmd, capture_output=True, text=True)
…How to Run Coverage Report and Generate HTML in Python
Use the coverage module to measure test coverage, save the report, and generate an HTML report in Python.
import coverage
import unittest
def add(a, b):
return a + b
class TestAdd(unittest.TestCase):
def test_add_positive(self):
self.assertEqual(add(2, 3), 5)
if __name__ == "__main__":
cov = coverage.Coverage(source=["__main__"])
cov.start()
suite = unittest.defaultTestLoader.loadTestsFro…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…Mock Python version with unittest.mock.patch
Use unittest.mock.patch to simulate a specific Python version and test version-dependent behavior.
import sys
import unittest
from unittest.mock import patch
class TestPythonVersion(unittest.TestCase):
@patch("sys.version_info", (3, 9, 0, "final", 0))
def test_python_version_pinned(self):
self.assertEqual(sys.version_info[:2], (3, 9))
print(f"Pinned version: {sys.version_info.major}.{sys.ve…Mock pdm build and publish in Python
Simulate pdm build and publish commands with unittest.mock to test packaging workflows without triggering real builds or uploads.
from unittest.mock import Mock, patch
import pdm
def build_package() -> str:
"""Simulate building a package with pdm."""
build_mock = Mock(return_value="dist/mypackage-0.1.0-py3-none-any.whl")
with patch.object(pdm, "build", build_mock):
result = pdm.build()
return result
def publish_packa…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.
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…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.
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…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.
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…How to Mock open() in Python for Reading File Data
This example shows how to mock Python's built-in open() function using unittest.mock to simulate file reading without touching the disk.
import builtins
from unittest.mock import patch
def read_file_data(filename):
with open(filename, 'r') as f:
return f.read()
def mock_read_data():
fake_data = "This is mocked file content"
class FakeFile:
def __enter__(self):
return self
def __exit__(self, *args):…How to Mock requests.get in Python
Mock requests.get with unittest.mock to test code that makes HTTP calls without hitting the network.
import requests
from unittest.mock import Mock, patch
def fetch_user_data(user_id):
response = requests.get(f"https://api.example.com/users/{user_id}")
return response.json()
def process_user(user_id):
mock_response = Mock()
mock_response.json.return_value = {"id": user_id, "name": "Alice", "age": 30…Browse by section
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