python-testing-patterns

Python Testing Patterns

Comprehensive guide to implementing robust testing strategies in Python using pytest, fixtures, mocking, parameterization, and test-driven development practices.

When to Use This Skill

• Writing unit tests for Python code
• Setting up test suites and test infrastructure
• Implementing test-driven development (TDD)
• Creating integration tests for APIs and services
• Mocking external dependencies and services
• Testing async code and concurrent operations
• Setting up continuous testing in CI/CD
• Implementing property-based testing
• Testing database operations
• Debugging failing tests

Core Concepts

1. Test Types

• Unit Tests: Test individual functions/classes in isolation
• Integration Tests: Test interaction between components
• Functional Tests: Test complete features end-to-end
• Performance Tests: Measure speed and resource usage

2. Test Structure (AAA Pattern)

• Arrange: Set up test data and preconditions
• Act: Execute the code under test
• Assert: Verify the results

3. Test Coverage

• Measure what code is exercised by tests
• Identify untested code paths
• Aim for meaningful coverage, not just high percentages

4. Test Isolation

• Tests should be independent
• No shared state between tests
• Each test should clean up after itself

Quick Start

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

def test_add():
    """Basic test example."""
    result = add(2, 3)
    assert result == 5

def test_add_negative():
    """Test with negative numbers."""
    assert add(-1, 1) == 0

# Run with: pytest test_example.py

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Testing Best Practices

Test Organization

# tests/
#   __init__.py
#   conftest.py           # Shared fixtures
#   test_unit/            # Unit tests
#     test_models.py
#     test_utils.py
#   test_integration/     # Integration tests
#     test_api.py
#     test_database.py
#   test_e2e/            # End-to-end tests
#     test_workflows.py