tdd-cycle

Test-driven development in Rails uses a Red-Green-Refactor cycle: write a failing RED test capturing desired behavior, implement minimal GREEN code to pass it, then safely REFACTOR while keeping tests green.

The best way is the Red-Green-Refactor workflow: capture desired behavior in a failing RED test, write the smallest GREEN implementation to pass it, then improve code structure while verifying tests stay green.

Choose test location based on what the feature touches: model tests for data logic, controller or system tests for requests, and service or job tests for specialized behavior verification across Rails components.

Tests break during refactoring when they verify implementation details rather than behavior. Focus tests on observable outcomes and run them iteratively after each small code change to catch failures immediately.

Yes, the workflow applies to building features across Rails models, controllers, services, and jobs. It requires test failure confirmation, minimal code changes, iterative refactoring with repeated test runs, and final whole-scope verification.

Common anti-patterns include testing implementation details instead of behavior and creating brittle or slow tests. Validate that RED steps truly fail and GREEN steps truly pass to maintain a reliable verification loop.