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How to Test Exceptions in Python with pytest.raises
Learn the pytest.raises pattern to assert that specific exceptions are raised and validate their messages.
import pytest
def divide(a: int, b: int) -> float:
if b == 0:
raise ValueError("Cannot divide by zero")
return a / b
def test_divide_by_zero_raises():
with pytest.raises(ValueError, match="Cannot divide by zero"):
divide(10, 0)
def test_divide_by_zero_raises_exact_match():
with py…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…Mock GCP storage bucket blob upload in Python
Simulate uploading a blob to a GCP Storage bucket for testing without hitting the cloud.
import io
from datetime import datetime
from unittest.mock import MagicMock, patch
class MockBlob:
"""Simulates a GCP storage blob for unit testing."""
def __init__(self, name):
self.name = name
self.uploaded_at = None
self.content = b""
def upload_from_file(self, file_obj):
…How to Parametrize Tests in Python with pytest
This code demonstrates how to use pytest's @pytest.mark.parametrize decorator to run a single test function against multiple input sets, ensuring comprehensive coverage with minimal code duplication.
import pytest
def multiply(a, b):
return a * b
@pytest.mark.parametrize("x, y, expected", [
(2, 3, 6),
(4, 5, 20),
(0, 10, 0),
(7, 1, 7),
])
def test_multiply(x, y, expected):
result = multiply(x, y)
assert result == expected, f"multiply({x}, {y}) = {result}, expected {expected}"
if _…How to Test HTTPX Async Client Pool Reuse with Mocks in Python
Mock an httpx.AsyncClient to verify connection pool reuse by asserting GET calls share a single client instance across concurrent async requests.
import asyncio
import httpx
from unittest.mock import AsyncMock, patch, Mock
async def fetch_with_pool(client, url, n_reuses=3):
results = []
for i in range(n_reuses):
resp = await client.get(url)
results.append(resp.status_code)
await asyncio.sleep(0) # yield to loop to mimic real us…Fix and Test a Regression Bug in Python with Unit Tests
This code implements a circle area function that raises ValueError for negative radii, then runs basic tests and a regression check for that edge case.
import math
def calculate_area(radius):
"""Calculate the area of a circle given its radius."""
if radius < 0:
raise ValueError("Radius cannot be negative")
return math.pi * radius ** 2
def main():
test_cases = [0, 1, 2.5, 5, 10]
print("Circle Area Calculator")
print("-" * 30)
…How to Flag Unexpected Diff Changes in Python
Compares two snapshot lists, detects unexpected differences, and returns a flag indicating whether the snapshot should be updated.
import difflib
def snapshot_diff(before, after, intentional_changes=None):
"""Compare snapshots and flag only unexpected differences."""
intentional_changes = intentional_changes or set()
diff = list(difflib.unified_diff(before, after, lineterm=""))
has_unexpected = False
for line in diff:
…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 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.
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…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…How to Parametrize pytest Tests with Multiple Input Cases in Python
This code shows how to use pytest's @pytest.mark.parametrize decorator to run the same test function across multiple input-output combinations, checking that an add function behaves correctly for each case.
import pytest
def add(a, b):
return a + b
@pytest.mark.parametrize("a,b,expected", [
(1, 2, 3),
(5, 5, 10),
(-1, 1, 0),
(0, 0, 0),
(10, -3, 7),
])
def test_add(a, b, expected):
assert add(a, b) == expected
if __name__ == "__main__":
pytest.main([__file__, "-v"])How to Write a Contract Test with Mock in Python
Use unittest.mock to verify a consumer's expectations match the provider's response shape in a Python contract test.
from unittest.mock import Mock
# Contract test: verify consumer expects data shape that provider delivers.
# We mock the provider and assert the consumer's calls match the agreed contract.
def fetch_user(provider_client, user_id):
"""Consumer code: expects provider to return {'id', 'name', 'email'}."""
respo…How to Write pytest Test Function Assert Equal in Python
Write three pytest test functions that assert the result of an add() function equals an expected numeric value.
import pytest
def add(a, b):
return a + b
def test_add_positive_numbers():
assert add(2, 3) == 5
def test_add_negative_numbers():
assert add(-1, -2) == -3
def test_add_mixed_numbers():
assert add(5, -3) == 2
if __name__ == "__main__":
pytest.main([__file__, "-v"])How to Mock zlib Compression for Cache Values in Python
Compress cache values with zlib and mock the compress function in unit tests to simulate cache behavior.
import zlib
from unittest.mock import patch
def compress_value(data: bytes) -> bytes:
"""Compress data using zlib and return the compressed bytes."""
return zlib.compress(data)
def decompress_value(compressed: bytes) -> bytes:
"""Decompress zlib data and return the original bytes."""
return zlib.deco…How to Mock Hive Support in PySpark with unittest.mock
This code demonstrates how to mock Hive support in a PySpark environment using unittest.mock to simulate SQL queries returning fixed data.
from unittest.mock import Mock, patch
def get_hive_tables(spark):
"""Mock Hive support by returning a fixed list of tables."""
return spark.sql("SHOW TABLES").collect()
class HiveTable:
"""Simple class that mimics a Hive table row."""
def __init__(self, database, tableName):
self.database =…How to Mock MLflow Model Registration in Python
Build a lightweight in-memory mock of MLflow's MlflowClient to test model registration, versioning, and stage transitions without a tracking server.
from mlflow.tracking import MlflowClient
from mlflow.entities import ModelVersion, Model
class MockMlflowClient:
"""Minimal mock of MlflowClient's model registration methods."""
def __init__(self):
self.registered_models = {}
self.model_versions = {}
def register_model(self, mod…How to Mock train_test_split in Python for Unit Testing
Build a lightweight mock of sklearn's train_test_split to unit test ML pipeline code without needing the full library or deterministic random state.
import numpy as np
from sklearn.model_selection import train_test_split
from unittest.mock import patch
def mock_train_test_split(X, y, test_size=0.25, random_state=None, **kwargs):
"""A simple mock implementation of train_test_split."""
n_samples = len(X)
n_test = int(n_samples * test_size)
n_train =…How to Calculate Minimum Sample Size for a T-Test in Python
Compute the minimum sample size per group for a two-sample t-test using effect size, significance level, and statistical power.
import math
from scipy.stats import norm
def min_sample_size(effect_size, alpha=0.05, power=0.8):
"""
Calculate minimum sample size for a two-sample t-test (equal groups).
Args:
effect_size: Cohen's d (standardized mean difference)
alpha: significance level (Type I error)
power: …How to Conduct a Two-Sample T-Test in Python
Performs Welch's t-test for two independent samples, computing the t-statistic, degrees of freedom, and p-value using NumPy and SciPy.
import numpy as np
def two_sample_t_test(sample1, sample2):
"""Perform Welch's t-test for two independent samples."""
n1, n2 = len(sample1), len(sample2)
mean1, mean2 = np.mean(sample1), np.mean(sample2)
var1, var2 = np.var(sample1, ddof=1), np.var(sample2, ddof=1)
# Standard error of difference
…How to Mock Time for Cache TTL Testing in Python
This code demonstrates how to test a cache's TTL expiration logic by mocking time.time with unittest.mock to control the passage of time.
import time
from unittest.mock import patch
class ConfigCache:
def __init__(self, ttl=60):
self.ttl = ttl
self._store = {}
self._timestamps = {}
def get(self, key):
if key not in self._store:
return None
if time.time() - self._timestamps[key] > self.ttl:
…How to Perform Intent-to-Treat Analysis in Python
Runs an intent-to-treat analysis on mock A/B test data, comparing outcomes by initial group assignment with a t-test for significance.
import pandas as pd
import numpy as np
def intent_to_treat_analysis(data):
"""Perform intent-to-treat (ITT) analysis.
ITT compares outcomes based on initial treatment assignment,
regardless of whether participants actually received the treatment.
"""
# Create a copy to avoid mutating the origina…How to Perform Welch's t-Test in Python
Calculate the Welch t-statistic and degrees of freedom for two samples with unequal variances using Python's statistics module.
import math
from statistics import mean, variance
def welch_t_test(sample1, sample2):
n1, n2 = len(sample1), len(sample2)
mean1, mean2 = mean(sample1), mean(sample2)
var1, var2 = variance(sample1), variance(sample2)
# Welch's t statistic
t_stat = (mean1 - mean2) / math.sqrt(var1 / n1 + var2 / n2…Browse by section
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