Integration and Functional Testing

Unit tests prove a class works in isolation with everything mocked. But mocks can lie — the real database, framework router, or HTTP layer behaves differently. Integration tests verify two or more real components wired together; functional tests exercise the application end-to-end through its public entry point (an HTTP request, a console command). This lesson positions and writes both.

A healthy suite is shaped like a pyramid:

• Many unit tests — fast, isolated, run constantly.
• Fewer integration tests — real DB/queue/cache, slower.
• Few functional/E2E tests — full stack, slowest, most brittle.

Inverting this (an 'ice-cream cone' of mostly E2E tests) yields a slow, flaky suite. Push coverage down whenever possible.