05 — Testing Strategies

The testing pyramid balances unit, integration, and E2E tests to build a suite that gives confidence for shipping. It emphasizes a broad base of fast unit tests, fewer integration tests, and a minimal layer of slow end-to-end tests.

Test doubles like mocks, stubs, and fakes isolate the system under test by replacing real dependencies. Effective use involves matching the double to the scenario: fakes for working implementations, stubs for state setup, and mocks for verifying interactions.

To safely refactor critical business logic, start by designing an automated testing strategy that covers the testing pyramid, implements TDD, and uses property-based testing to verify existing functionality and prevent regressions before making changes.

Test-Driven Development (TDD) works well with property-based testing by combining example-driven design with broad, randomized input verification. TDD guides the interface design while property-based testing validates edge cases and invariants across generated data.

Common pitfalls in automated testing strategy include over-relying on slow E2E tests, using the wrong test doubles, and writing brittle tests that break during refactoring. The goal is writing tests that provide confidence to change code without fear of regressions.