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Testing & modern typing

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

4 matches

Characterization Test for Legacy Python Code

Capture the exact output of a legacy Python function for known inputs, creating a characterization test that documents current behavior before refactoring.

characterization-testing legacy-code testing

Python

def legacy_behavior(value):
    """Legacy function that returns a tuple with unconventional types."""
    if value == "special":
        return None, "legacy-special"
    elif value > 100:
        return value, "large"
    elif value > 0:
        return value * 2, "positive-doubled"
    elif value == 0:
     …

14 0 Open

Testing & modern typing medium

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.

pytest benchmark mock

Python

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:…

14 0 Open

Testing & modern typing medium

How to Compare Execution Speed Between Python Functions

Measure and compare the average execution time of multiple Python functions using a reusable benchmark helper with time.perf_counter.

performance benchmarking time

Python

import time
import random

def method_a(values):
    """Sort using built-in sorted."""
    return sorted(values)

def method_b(values):
    """Sort using list's sort method."""
    values_copy = values[:]
    values_copy.sort()
    return values_copy

def method_c(values):
    """Sort manually using bubble sort (slow,…

38 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 = …

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