Testing Best Practices: pytest and TDD

Learning Objectives: After this lesson, you'll master pytest with fixtures, parametrization, and mocking, understand test-driven development, achieve meaningful coverage, and write maintainable tests.

Why Testing Matters

Tests are insurance for your code—they catch bugs before users do and give you confidence to refactor.

The Testing Pyramid

pytest Fundamentals

Basic Test Structure

Test Organization

Fixtures: Setup and Teardown

Fixtures provide reusable test setup and cleanup.

Basic Fixtures

Fixture Scopes

Parametrization: Test Multiple Cases

Mocking: Isolate Units

Patching

Test-Driven Development (TDD)

Testing Async Code

Coverage and Quality

Best Practices

Practice Exercises

Exercise 1: Test a Shopping Cart

Key Takeaways

Testing Checklist

• Unit tests for business logic
• Edge cases and error handling
• Integration tests for components
• Mocks for external dependencies
• Async tests with pytest-asyncio
• Coverage > 80% for critical code
• Fast test suite (< 1 minute)
• CI pipeline runs all tests

Next Steps

In the next lesson, we'll explore Design Patterns in Python—implement classic patterns like Factory, Strategy, Observer, and Dependency Injection the Pythonic way.

Ready to write elegant code? Design patterns await!