Integration testing

Integration testing verifies how different parts of your application work together in real-world scenarios. It focuses on testing the connections, data flow, and interactions between modules or components after they've been combined into a functioning system. 

A common example is testing user authentication—verifying that the login form, authentication service, user database, and session management all work together properly. Another example is testing an e-commerce checkout flow, where you verify that inventory updates, payment processing, order creation, and email notifications all function correctly as an end-to-end process. 

While unit tests verify individual components, integration testing catches issues that only appear when those components interact. These can include data formatting mismatches, timing problems, configuration errors, and interface incompatibilities. Finding these issues early prevents costly bugs in production and helps ensure your system works reliably as a whole. 

Key challenges include: Setting up and maintaining realistic test environments with all required dependencies Managing test data across interconnected components Handling external services and third-party integrations Debugging failures when multiple components are involved Dealing with asynchronous operations and timing issues These can be addressed using techniques like containerization, service virtualization, and carefully structured test environments.