Reference library

Testing & modern typing

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

1 match
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

Browse by section

Each section groups closely related Python snippets.

Testing & modern typing — Python code examples

What you will find here

This page collects testing & modern typing snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.

Samples vs tutorials and challenges

Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.

Related coding tools

Free online Python IDE Write and run Python in your browser — no install. Free Python code formatter Format with autopep8 — side-by-side PEP 8 cleanup. Python code samples Copy-ready snippets to study and run in the IDE.