test-driven-development

Unit tests before implementing new features require a red-green-refactor workflow: create a failing test that defines expected behavior, write the minimal code to pass it, then refactor while keeping the suite green.

The red-green-refactor workflow in test-driven development is a cycle of writing a failing test, implementing the smallest code change to make it pass, and then cleaning up the code while ensuring behavior remains validated.

To reproduce a bug with a failing test, write a test that explicitly demonstrates the defect before touching production code, confirming the test fails for the right reason, then apply the smallest fix to make it pass.

Over-mocking dependencies makes unit tests fragile because it decouples tests from real behavior, leading to false positives; tests should validate actual outcomes rather than interaction details or test-only production methods.

Yes, you can use test-driven development for refactoring existing code by relying on a green test suite to validate that behavior-preserving cleanup and structural changes do not introduce regressions.

The best way to avoid adding test-only methods during TDD is to enforce minimal implementations that rely on public behavior validation rather than exposing internal methods solely for unit test coverage.