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Testing & modern typing

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

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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…

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Testing & modern typing easy

How to Sort Data in Python

Sort sequences with type-safe helpers that handle mixed data with a string fallback.

sorting typing protocol

Python

from typing import Any, TypeVar, Protocol, Sequence, Iterable

T = TypeVar("T")
Comparable = TypeVar("Comparable", bound="Comparable")

class Sortable(Protocol):
    def __lt__(self, other: Any) -> bool: ...

S = TypeVar("S", bound=Sortable)

def sort_data(data: Sequence[S], *, reverse: bool = False) -> list[S]:
    "…

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Testing & modern typing easy

How to Use Literal Type Hints in Python

Use typing.Literal to restrict a function parameter to specific allowed string values and get static type checking.

typing type-hints literal

Python

from typing import Literal

def get_status_message(status: Literal["active", "inactive", "pending"]) -> str:
    """Return a message based on the status value."""
    if status == "active":
        return "Account is active"
    elif status == "inactive":
        return "Account is inactive"
    else:
        return "…

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Testing & modern typing easy

How to Use mock.assert_called_with in Python

Verify that a MagicMock received a call with specific positional and keyword arguments using assert_called_with in unittest.

unittest mock testing

Python

import unittest
from unittest.mock import MagicMock

class TestMockAssertions(unittest.TestCase):
    def test_assert_called_with(self):
        # Create a mock object
        mock = MagicMock()

        # Call the mock with specific arguments
        mock.send_email("alice@example.com", subject="Greetings", body="Hel…

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Testing & modern typing easy

How to Verify Formatted Output with an Approval Test in Python

Write a small Python approval test that verifies a function's exact formatted output using unittest.

approval-testing unittest formatting

Python

import sys
from io import StringIO
import unittest

def generate_output(name, score):
    return f"Player: {name} | Score: {score:03d}"

class TestFormattedOutput(unittest.TestCase):
    def test_output_format(self):
        expected = "Player: Alice | Score: 042"
        result = generate_output("Alice", 42)
        …

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Testing & modern typing easy

How to freeze time in Python tests with freezegun

Use the freezegun decorator to freeze datetime.now() at a fixed timestamp so tests that depend on current time run deterministically.

freezegun datetime testing

Python

from datetime import datetime
from freezegun import freeze_time


@freeze_time("2024-01-15 12:30:00")
def test_frozen_time():
    now = datetime.now()
    return now


if __name__ == "__main__":
    result = test_frozen_time()
    print(result)

15 0 Open

Testing & modern typing easy

How to use unittest mock side_effect with a sequence in Python

Demonstrates using Mock.side_effect with a list to return different values per call and raise an exception at a specific call in unittest.

unittest mock side_effect

Python

import unittest
from unittest.mock import Mock

class TestMockSideEffectSequence(unittest.TestCase):
    def test_side_effect_sequence(self):
        mock = Mock()
        mock.side_effect = [1, 2, 3, Exception("boom")]
        
        self.assertEqual(mock(), 1)
        self.assertEqual(mock(), 2)
        self.asser…

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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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