Reference library

Testing & modern typing

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

5 matches

Dataclass with Type Hints Fields in Python

Create a data class with typed fields and default values, then instantiate and inspect it.

from dataclasses import dataclass


@dataclass
class Person:
    name: str
    age: int
    email: str = "unknown@example.com"
    is_active: bool = True


if __name__ == "__main__":
    person = Person(name="Alice", age=30)
    print(person)
    print(f"Name: {person.name}, Age: {person.age}, Email: {person.email}, A…

12 0 Open

Testing & modern typing medium

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.

unittest mock patch

Python

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…

14 0 Open

Testing & modern typing medium

How to Use Stubs, Fakes, Spies, and Mocks in Python Testing

Implement four types of test doubles — stubs, fakes, spies, and mocks — as subclasses of a PaymentGateway interface to replace real dependencies during testing.

testing mocks stubs

Python

class PaymentGateway:
    def charge(self, amount):
        raise NotImplementedError


class StubPaymentGateway(PaymentGateway):
    """Returns a fixed response without any logic."""
    def charge(self, amount):
        return {"success": True, "transaction_id": "stub-12345"}


class FakePaymentGateway(PaymentGatewa…

12 0 Open

Testing & modern typing easy

How to Use TypedDict and Dataclasses in Python

Create typed data structures with TypedDict and dataclasses, then use them as helper functions for describing objects in a type-safe way.

typing typdict dataclass

Python

from typing import TypedDict, NotRequired, Optional
from dataclasses import dataclass


class User(TypedDict):
    name: str
    age: NotRequired[int]
    email: Optional[str]


@dataclass
class Product:
    id: int
    title: str
    price: float = 0.0


def describe_user(user: User) -> str:
    age = user.get("age",…

12 0 Open

Testing & modern typing easy

How to Validate Dataclass Fields with Python Type Hints

A beginner-friendly helper that checks if instance attributes match their declared type hints using dataclasses and get_type_hints.

dataclasses type-hints validation

Python

from typing import Any, TypeVar, get_type_hints
from dataclasses import dataclass

T = TypeVar("T")

@dataclass
class User:
    name: str
    age: int
    email: str

def validate_fields(obj: Any) -> dict[str, bool]:
    """Check if object attributes match declared type hints."""
    hints = get_type_hints(obj.__class…

13 0 Open

Browse by section

Each section groups closely related Python snippets.