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System design patterns

Sharding, load balancing, CAP tradeoffs, and scaling patterns — interview and production ready.

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How to Mock Hexagonal Architecture Ports and Adapters in Python

Mock an email adapter in a hexagonal architecture with unittest.mock to test business logic in isolation.

hexagonal-architecture unittest-mock dependency-injection

from unittest.mock import Mock

class EmailService:
    def send(self, recipient, message):
        raise NotImplementedError

class OrderProcessor:
    def __init__(self, email_service):
        self.email_service = email_service
    
    def process_order(self, order_id, customer_email):
        # Business logic
   …

15 0 Open

System design patterns easy

How to Mock a Metrics Decorator in Python with unittest.mock

This code demonstrates a timing decorator that wraps a function to measure execution time and prints the duration, with a unit test using unittest.mock to patch the print function and assert it was called.

decorators unittest.mock metrics

Python

import time
from functools import wraps
from unittest.mock import patch

def add_metrics(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        elapsed = time.perf_counter() - start
        print(f"{func.__name__} took {elapsed:.6f}s…

15 0 Open

System design patterns medium

How to Mock a Timeout per Dependency Call in Python

This code demonstrates how to simulate and test per-call timeouts for external dependencies using Python's unittest.mock and a simple timing wrapper.

mock timeout unittest

Python

```python
import time
from unittest.mock import Mock, patch

def call_dependency(dependency, timeout):
    start = time.time()
    result = dependency.call()
    elapsed = time.time() - start
    if elapsed > timeout:
        raise TimeoutError(f"Dependency call took {elapsed:.2f}s, exceeding timeout {timeout}s")
    …

14 0 Open

System design patterns medium

Mock Unit of Work commit and rollback in Python

Verify that a Unit of Work pattern commits on success and rolls back on failure using unittest.mock in Python.

unit-of-work mocking testing

Python

from unittest import mock


class UnitOfWork:
    def __init__(self):
        self.committed = False
        self.rolled_back = False

    def commit(self):
        self.committed = True
        print("Commit executed")

    def rollback(self):
        self.rolled_back = True
        print("Rollback executed")


def b…

13 0 Open

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