Barend Linders - From mocking to rocking your tests with testcontainers | PyData Amsterdam 2024

Testcontainers is an open source library that allows spinning up Docker containers for integration testing, originally created for Java in 2015 but now supports 10+ languages

Key benefits:

• Enables “integration test light” capabilities between unit tests and full integration tests
• Containers are managed automatically (startup/shutdown)
• Provides realistic test environments while keeping tests local
• Supports many common services out of the box (Redis, PostgreSQL, etc)
• Can help speed up development feedback loops vs full integration testing

Best practices:

• Use primarily for black box testing scenarios
• Be mindful of container startup overhead and state management
• Consider session scoping to reuse containers across tests
• Can use config files and scripts to seed test data
• Good for testing service interactions without mocking

Limitations to consider:

• Additional overhead from container management
• May not 100% match production environment
• Need Docker available for tests to run
• Can be more complex to setup than simple mocks
• May require CI/CD environment considerations

The library helps address common testing challenges:

• Managing external dependencies
• Providing realistic test environments
• Reducing reliance on mocks
• Enabling faster development cycles
• Simplifying integration testing

Works well with pytest fixtures and can be integrated into existing test suites while still maintaining the benefits of containment and isolation