test-driven-development

Test-driven development starts by writing one failing test that specifies expected behavior, verifying the failure, making the smallest code change to pass it, then refactoring. This red-green-refactor cycle ensures reliable behavior specification and regression protection across application codebases.

Writing tests after implementation often leads to testing mock existence instead of actual product logic. Test-driven development prevents this by requiring real-behavior tests upfront, avoiding test-after shortcuts, incomplete mocks, and test-only production methods that fail to catch mistakes before they spread into production.

The best way to write unit tests for behavior changes is to define the expected behavior first with a failing test. This behavior-focused testing approach prefers real behavior over mock-heavy assertions, ensuring safer code changes and explicit coverage of edge cases during refactoring.

Yes, test-driven development works for fixing bugs and regressions by making the failing test the starting point. You define the expected behavior first, verify the failure, implement the minimum code to pass the test, and keep coverage aligned with actual outcomes to prevent future regressions.

To avoid over-mocking when writing unit tests, prefer real behavior over mock-heavy assertions and avoid testing mock existence instead of product logic. Test-driven development includes anti-pattern guardrails to detect incomplete mocks, over-mocking, and test-only production methods.