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Module 09: Testing Async Code

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Stub module — Full content to be generated. This file defines the scope and prerequisites so the topic roadmap is complete.

Overview

Testing async code has unique challenges: test functions must be coroutines, mock objects must support await, event loop lifecycle must be managed correctly, and timeouts and cancellation must be testable. This module covers pytest-asyncio as the standard test framework for async Python, unittest.mock.AsyncMock, and strategies for testing the hardest async scenarios: timeouts, retries, cancellation, and integration with databases and external services.

Table of Contents

  1. Overview
  2. Prerequisites
  3. Objectives
  4. Theory
  5. Key Concepts
  6. Examples
  7. Common Pitfalls
  8. Cross-Links
  9. Summary

Prerequisites

  • Module 08: Async Databases (for integration test examples)
  • Module 06: Structured Concurrency
  • Basic familiarity with pytest and unittest.mock

Objectives

By the end of this module, you will be able to:

  1. Write async test functions using pytest-asyncio
  2. Configure pytest-asyncio event loop scope (function, class, module, session)
  3. Mock async functions using unittest.mock.AsyncMock
  4. Test timeout behavior using pytest.raises(asyncio.TimeoutError)
  5. Test cancellation handling in coroutines
  6. Write integration tests that use async database fixtures
  7. Use anyio with pytest-anyio for framework-agnostic test suites

Theory

Full content to be generated. Topics to cover:

  • pytest-asyncio: @pytest.mark.asyncio, asyncio_mode = "auto" configuration
  • Event loop scoping: function-scoped vs session-scoped loops; performance implications
  • AsyncMock: creating, configuring side effects, asserting calls
  • Patching async context managers with AsyncMock
  • Testing timeouts: using asyncio.timeout() in test scenarios
  • Testing cancellation: task.cancel() + pytest.raises(asyncio.CancelledError)
  • Async fixtures: database connection fixtures with proper cleanup
  • pytest-anyio: writing tests that run on both asyncio and Trio

Key Concepts

To be filled in when this module is fully generated.

Examples

To be filled in when this module is fully generated.

Common Pitfalls

To be filled in when this module is fully generated.

  • [[async-python/modules/08_async-databases]] — prerequisite; integration test patterns
  • [[async-python/modules/10_production-patterns]] — tested production components
  • [[async-python/modules/11_capstone-project]] — capstone requires a test suite

Summary

To be filled in when this module is fully generated.