🧪 PythonPyTestTutorial

Industry-Grade PyTest (Sync + Async) for FastAPI Backends

📌 Overview

This repository demonstrates production-ready testing practices using PyTest for modern Python backends. It focuses on real-world FastAPI and async testing patterns, not just basic unit tests.

The project is designed so that HR, interviewers, and senior engineers can clearly see hands-on expertise in:

• PyTest fundamentals
• Async testing
• FastAPI endpoint testing
• Dependency isolation
• Mocking external systems
• CI-friendly deterministic tests

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🎯 What This Project Demonstrates

✔ PyTest fundamentals (assertions, exceptions, discovery rules)
✔ Clean test organization & naming conventions
✔ Fixtures, scopes, and shared fixtures (conftest.py)
✔ Parametrized tests & markers for CI pipelines
✔ Monkeypatch & mocking (APIs, env vars, time, UUID, randomness)
✔ Sync + Async test patterns
✔ FastAPI async endpoint testing (without running a real server)
✔ Dependency overrides (Auth, DB, Redis patterns)
✔ Async database isolation (transaction rollback pattern)
✔ Background task & Celery-like job testing strategies

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🏗️ Project Structure

PythonPyTestTutorial/
├── app/
│   ├── main.py                  # FastAPI app
│   ├── dependencies.py          # Auth / dependency examples
│   ├── async_math.py
│   ├── async_resource.py
│   ├── fake_async_db.py
│   ├── api_client.py
│   ├── user_service.py
│   ├── background_tasks.py
│   ├── time_service.py
│   ├── id_service.py
│   └── random_service.py
│
├── tests/
│   ├── unit/
│   │   ├── test_topic_1_*        # PyTest basics
│   │   ├── test_topic_2_*        # Fixtures, mocks, parametrization
│   │   ├── test_topic_3_*        # Async, FastAPI, DB, background tasks
│   ├── conftest.py               # Shared fixtures
│
├── pytest.ini                    # Central PyTest configuration
└── README.md

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🧠 Key Concepts Covered

🔹 PyTest Core

• Test discovery rules
• Assertions & exception testing
• CLI usage & failure analysis
• Test organization & naming

🔹 Fixtures & Mocking

• Fixture scopes (function / module / session)
• Setup & teardown with yield
• Shared fixtures using conftest.py
• Parametrized tests
• Markers for selective test runs
• Monkeypatch for dependency isolation

🔹 Async & FastAPI Testing

• pytest-asyncio
• Async fixtures & lifecycle management
• FastAPI endpoint testing with httpx.AsyncClient + ASGITransport
• Dependency overrides for auth, DB, Redis
• Async DB transaction rollback pattern
• Background task & worker testing strategy

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⚙️ How to Run Tests

Run all tests:

pytest

Run only unit tests:

pytest -m unit

Verbose mode (default via pytest.ini):

pytest -v

🧩 Tech Stack

• Python 3.12
• PyTest
• pytest-asyncio
• FastAPI
• httpx
• Async programming patterns

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🏁 Final Note

This repository is built to reflect real production testing scenarios, not toy examples. All patterns demonstrated here are directly applicable to enterprise FastAPI and microservice backends.