tdd

Test-driven development begins by defining the first public behavior your feature must exhibit. You write a failing test against the public interface, implement the minimal code to pass it, and then refactor safely while keeping the behavior validated.

The red-green-refactor loop is a test-driven cycle where you write a failing test, implement minimal code to pass it, then refactor safely. It improves reliability by verifying observable behavior early and preventing overbuilt, brittle implementation logic.

You should mock dependencies at boundary limits during integration-style tests. Deciding what behaviors matter most and mocking only external collaborators keeps tests resilient through refactors and focused on observable public outcomes.

Behavior-focused testing targets public interfaces and observable outcomes instead of private methods. You validate user-visible behavior through integration-style tests, ensuring your test suite remains resilient during post-green refactoring and internal implementation changes.

Test-driven development effectively fixes bugs by writing a failing test that reproduces the incorrect behavior first. You then apply minimal incremental code changes to correct the logic and ensure the behavior-focused validation passes before refactoring.

You should avoid test-driven development for refactoring when existing tests are tightly coupled to private implementation details rather than public interfaces. Refactoring requires behavior-focused validation, so brittle implementation-driven tests will break during structural changes.