tdd

Test-driven development is implemented through the red-green-refactor loop, starting with writing integration-style tests for observable behavior before writing the actual code, then incrementally building until tests pass, and refactoring safely. This methodology ensures software is built with verifiable behavior and maintainability.

Testing observable behavior involves writing integration-style tests that interact exclusively with public interfaces. This behavior-driven testing approach avoids brittle implementation-detail tests by focusing on what the software does from the outside, ensuring refactoring remains safe without breaking existing test suites.

The red-green-refactor methodology is needed when developing new features or fixing bugs to ensure software maintainability. By guiding development through planning, tracer bullets, and incremental loops, it builds confidence that each piece functions as expected before moving forward.

Test-driven development works for fixing bugs by applying the red-green-refactor loop to write failing tests that reproduce the defect. This process verifies the observable behavior through public interfaces, ensuring the fix resolves the issue without introducing brittle implementation-detail tests.

Test suites break during code refactoring when tests are tightly coupled to implementation details rather than observable behavior. By shifting to integration-style tests that verify public interfaces, you avoid brittle tests and ensure refactoring remains safe and maintainable.