pytest

pytest - Professional Python Testing

Overview

pytest is the industry-standard Python testing framework, offering powerful features like fixtures, parametrization, markers, plugins, and seamless integration with FastAPI, Django, and Flask. It provides a simple, scalable approach to testing from unit tests to complex integration scenarios.

Key Features:

• Fixture system for dependency injection
• Parametrization for data-driven tests
• Rich assertion introspection (no need for self.assertEqual)
• Plugin ecosystem (pytest-cov, pytest-asyncio, pytest-mock, pytest-django)
• Async/await support
• Parallel test execution with pytest-xdist
• Test discovery and organization
• Detailed failure reporting

Installation:

# Basic pytest
pip install pytest

# With common plugins
pip install pytest pytest-cov pytest-asyncio pytest-mock

# For FastAPI testing
pip install pytest httpx pytest-asyncio

# For Django testing
pip install pytest pytest-django

# For async databases
pip install pytest-asyncio aiosqlite

Basic Testing Patterns

1. Simple Test Functions

# test_math.py
def add(a, b):
    return a + b

def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0
    assert add(0, 0) == 0

def test_add_negative():
    assert add(-2, -3) == -5

Run tests:

# Discover and run all tests
pytest

# Verbose output
pytest -v

# Show print statements
pytest -s

# Run specific test file
pytest test_math.py

# Run specific test function
pytest test_math.py::test_add

2. Test Classes for Organization

# test_calculator.py
class Calculator:
    def add(self, a, b):
        return a + b

    def multiply(self, a, b):
        return a * b

class TestCalculator:
    def test_add(self):
        calc = Calculator()
        assert calc.add(2, 3) == 5

    def test_multiply(self):
        calc = Calculator()
        assert calc.multiply(4, 5) == 20

    def test_add_negative(self):
        calc = Calculator()
        assert calc.add(-1, -1) == -2