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Testing & modern typing

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

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Dependency Injection in Python for Testability

Inject a config dependency into a service so you can swap a real environment-based config for a fake one in tests.

import os


class Config:
    """Simple config loader that can be easily faked in tests."""
    def get(self, key, default=None):
        return os.environ.get(key, default)


class UserService:
    def __init__(self, config):
        self.config = config

    def get_timeout(self):
        return int(self.config.get(…

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Testing & modern typing easy

How to Mock requests.get in Python

Mock requests.get with unittest.mock to test code that makes HTTP calls without hitting the network.

mocking requests unit-testing

Python

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…

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Testing & modern typing easy

Interface Segregation with Fake Test Implementations in Python

Defines segregated abstract interfaces (Printer, Scanner) and uses a FakePrinter to record calls for unit testing without real resources.

abc interface-segregation testing

Python

from abc import ABC, abstractmethod


class Printer(ABC):
    @abstractmethod
    def print_document(self, doc: str) -> str:
        pass


class Scanner(ABC):
    @abstractmethod
    def scan_document(self) -> str:
        pass


class MultiFunctionPrinter(Printer, Scanner):
    def print_document(self, doc: str) -> …

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Testing & modern typing easy

Mock datetime with time-machine in Python

Use the time-machine library to travel to a fixed datetime when running tests or scripts, mocking datetime.utcnow().

testing datetime mock

Python

from time_machine import travel
from datetime import datetime


@travel("2020-01-01 10:30:00")
def check_date():
    return datetime.utcnow()


if __name__ == "__main__":
    print(check_date())

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